Gravity: Lesson Plans

Jodrell Bank Discovery Centre Big Science: Big Telescopeswww.jodrellbank.net

Gravity: Lesson PlansA series of 2-3 lessons on the nature of gravity for Key Stage 3 pupils.

This lesson plan has been developed by the Jodrell Bank Discovery Centre as part of the Science and Technology Facilities Council’s (STFC) Science and Society Large Award project Big Science: Big Telescopes.

This lesson plan is free for teachers to download and share.

This lesson/series of lessons is designed to excite and inspire pupils by engaging them with examples of the ‘Big Science’ carried out with the ‘Big Telescopes’ funded by STFC, whilst also teaching key points from the KS3 2014 Science National Curriculum.

Some of the Big Telescopes with funding from STFC include the VLT (Very Large Telescope), ALMA (Atacama Large Millimetre/sub-millimetre Array), e-MERLIN (the UK's facility for high resolution radio astronomy observations), E-ELT (European Extremely Large Telescope) and SKA (Square Kilometre Array).

The Lovell telescope at Jodrell Bank, part of e-MERLIN.

http://www.jodrellbank.net/

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/239134/SECONDARY_national_curriculum_-_Science.pdf


Table of Contents

Introduction 3

Lesson Plan Part 1: Gravity on Earth 4

Lesson Plan Part 2: Big Telescopes 9

Lesson Plan Part 3: Gravity in Space 13

Practical Activity 1 17

Practical Activity 2 19

Answers to the Mass and Weight Worksheet 21

Answers to the Part 1 Review 22

Answers to the Part 3 Review 22

Additional Resources 23

Use of Images 23



IntroductionGravity is one of the four fundamental forces in the universe. The force of gravity was first described mathematically by Sir Isaac Newton in 1687. His theory described how objects feeling the force of gravity behaved, but Newton could not explain gravity’s origins. This came in 1916, when Albert Einstein published his theory of General Relativity, which described gravity as the result of mass curving space-time around it.

Through observations made by Big Telescopes, our understanding of gravity is tested. These observations include examining how objects like planets and stars move in space and the way light bends around massive objects like galaxies. This is still an open area of research as there are many mysteries remaining in the universe. The answers to some of these mysteries may force us to update our current ideas of gravity.

These lesson plans are presented in three sections: Gravity on Earth, Big Telescopes and Gravity in Space. Depending on the length of lessons in your school these could be delivered as a single lesson, or split into a series of two or three separate lessons.

Within this lesson/series of lessons your pupils will learn about the classical force of gravity, put forward by Newton. They will learn the difference between mass and weight, the equation that relates the two and perform an investigation into the strength of gravity on Earth. Pupils will then use a 3D model of gravity, similar to the model of General Relativity put forward by Einstein, to better imagine the force of gravity and its effects.

All pupil materials are provided, including suggestions on how these could be differentiated for different abilities. At the end of sections one and three there are review questions that assess the learning objectives of those sections.

An artist’s impression, using real data from the European VLT telescope, of the stars which orbit the supermassive black-hole at the centre of the Milky Way galaxy and the cloud of gas which is falling into it.



Part 1: Gravity on Earth

Learning Objectives

All Comprehend the terms mass and weight Use the formula weight = mass x gravity Run a scientific investigation, taking repeat readings to collect meaningful results

Most Identify anomalous data to generate more accurate results Compare everyday evidence with evidence from the Moon to conclude air resistance prevents objects falling at the same rate

Some Rearrange the formula weight = mass x gravity Analyse data to conclude that objects fall at the same rate regardless of mass (depending on choice of practical activity)

Suggested timeline of activities (times dependent on group)

Time & Activity Activity details Slide Teaching notes Differentiation

0-3 mins

Introduction

Introduce topic, structure of lesson and lesson objectives (if required).

1 & 2

Part 1 focuses on our experience of gravity on Earth and includes a practical investigation to measure the strength of gravity on Earth.

Part 2 describes how Big Telescopes are used to collect data about objects in space.

Part 3 uses a model to investigate how gravity behaves over large distances between planets and stars.

N/A

3-8 mins

Part 1: Starter

Watch Felix Baumgartner’s record breaking jump in 2012.

3

Use the hyperlink on the slide to be taken to the official video on YouTube.

Felix Baumgartner is an Austrian skydiver. On 14th October 2012, he set the world record for skydiving by falling from 39 kilometres (24 miles) above the Earth’s surface. On his descent he reached an estimated speed of 1,357.64 km/h (843.6 mph), or Mach 1.25. He became the first person to break the sound barrier without vehicular

N/A



power.

8-10 mins

Introduce Newton and mass

Introduce Newton’s theory of gravity and set the lesson in historical context.

Define the term mass.

4

Newton developed the first mathematical description of the force of gravity. Newton said that he started thinking about gravity after watching an apple fall from a tree (it did not actually hit him on the head, as it is often claimed!). After much work he realised it was the same force that was holding the Moon in orbit around the Earth. His theory perfectly described the force between the Earth and Moon and how they moved.

NB: Newton did not discover gravity; this is a common misconception. He was the first to realise that gravity extended out into space; that it was gravity which kept the Moon in orbit around the Earth and the planets in orbit around the Sun. Previous to this, it was thought to perhaps be a magnetic force.

N/A

5

Newton realised that any object which has mass produces a force of gravity and attracts other objects with mass. The size of that force increase as the object’s mass increases.

Mass refers to the amount of matter an object is made from. Mass is measured in grams and kilograms.

N/A

10-12 mins

Introduce weight

Assess pupils' prior knowledge of weight.

6

Present pupils with the image of the dog (there is no reason for it to be a dog, I just like dogs). Ask them to choose the force acting on the dog (represented by a force arrow), and then name the force. Most pupils would probably name the force as ‘gravity’. This answer would be accepted in most KS3 tests; however the correct name for the force is ‘weight’. This activity requires pupils to have a prior knowledge of representing forces with force arrows.

Pupils could vote on their choices using voting cards, or mini-whiteboards. For higher achieving pupils the options could be deleted and pupils could draw their answer on the board, if using an IWB. Alternatively side 6 could be printed out for pupils, to answer



individually or in pairs/groups.

12-14 mins

Summary

Summarise the difference between the terms mass and weight.

7

Summarise the difference between the terms mass and weight using the table and introduce the equation which relates the two.Some pupils often struggle to understand ‘mass’ and the difference from ‘weight’, since the terms are used in everyday life interchangeably.

Peer support could be used for pupils who are struggling. Pupils could be asked to consider situations where weight would be different, but mass the same.

14-20 mins

Questions

Assess pupils understanding of mass and weight, by using the equation.

N/A

See the accompanying document ‘Mass and Weight Worksheet’. The questions require pupils to use the formula W=mg. The Earth is not used as an example on this worksheet, since measuring the strength of gravity on Earth is the objective of the following practical activity. For the answers go to Answers to the Mass and Weight worksheet.

The questions supplied become gradually harder. Select and use the questions suitable for your group.

20-32 mins

Practical activity 1

Practical investigation measuring the strength of gravity on Earth.

8See section Practical activity 1 for more information about the various practical activities available at this point.

Pupils could be placed in mixed ability groups, for peer support. Alternatively, different groups could complete different experiments based on their achievement. Pupils could then compare to see if different methods gave the same results.



32-36 mins

Determine anomalous readings

Pupils identify and delete anomalous readings.

9

Depending on which practical activity your pupils have followed, they may need to identify and delete anomalous readings. This will be especially important if they have completed a data logging or freefall timing activity.

Pupils could decide within groups which are the anomalous readings. Alternatively pupils could take copies of the results and analyse them individually.

36-40 mins

Reflect on practical

Pupils review their findings and methodology.

10

Pupils bring together their results, to form a class average. The first three questions on slide 10 provide pupils with a structure to evaluate their results and their methodology.

The fourth question has been specifically included if you have completed a freefall practical and have used differing masses of similar sizes. In this case, acceleration results should be independent of mass (depending on quality of results) and some pupils may be able to discern this.

If you have completed a freefall practical and used differing masses of similar sizes, some higher achieving pupils may be able to recognise that acceleration of fall is independent of mass (depending on the quality of pupils’ results).

40-42 mins

Consider a popular misconception: that heavy objects fall quicker than lighter objects

Test prior knowledge of misconception.

11

If pupils concluded that freefall acceleration is independent of mass in the above practical, this can be linked to the activity below.

Ask pupils to consider a hammer and a feather. Which one has the largest weight force? Which one will hit the ground first when dropped?Why?

The hammer will have the largest weight (shown by the larger force arrow). On Earth, the hammer will fall to the ground quickest, but this is not because it is heavier.

Pupils could vote on the correct answer, maybe using voting cards, or mini-whiteboards.Higher achieving pupils could be asked to explain why the hammer falls to Earth quicker, to better assess prior knowledge.



42-46 mins

Address misconception that heavy objects fall quicker than lighter objects

Show evidence contradicting misconception.

12

In 1971, during the Apollo 15 mission on the Moon, Commander David Scott dropped a 1.3 kilogram hammer and a 3 gram feather from the same height.

Click the link to watch this video on YouTube. The quality is not great due to the 1970s recording technology. Hopefully it can be seen that both objects hit the Moon’s surface at the same time.

It’s possible to complete this as a demonstration in the classroom, with a ‘guinea and feather tube’ and a vacuum pump1.

Pupils could be asked to predict what will happen. Higher achieving pupils could be asked to rationalise their choice, lower achieving pupils could vote on a number of multiple choice options.

Pupils re-examine evidence based on new knowledge.

13

Ask pupils to re-evaluate everyday experience, with new understanding.

The only reason that a feather falls slower than a hammer on the Earth is that air resistance has much more of an effect on the feather. The Moon on the other hand is a vacuum. Since it has no atmosphere, there is no air resistance slowing the feather’s descent.

Some pupils may be able to answer this question directly. Others may require further support, such as a list of differences between the Moon and Earth. Pupils could answer in groups, or think-pair-share.

46-50 mins

Review of Part 1

Assess whether learning objectives have been met.

14

To assess the learning objectives of part 1, pupils can answer the six questions presented on slide 14.

See Answers to the Part 1 Review for the answers.

Pupils could peer assess their answers and suggest improvements where necessary.

Part 2: Big Telescopes1 An example of this experiment being done can be found at https://www.youtube.com/watch?v=clom4DdnFfM


https://www.youtube.com/watch?v=clom4DdnFfM


Learning Objectives

All Set 'Part 3: Gravity in Space' in a real-world, global context Understand that science is ongoing and new scientific projects are underway Inspire pupils with the scale and scope of scientific enquiry

Most Comprehend that visible light is not the only sort of wave that travels through space and that other waves show different thingsSome List the advantages of building big telescopes



0-2 mins

Introduce Part 2

Introduce idea that astronomers need to collect data.Introduce learning objectives if required.

15

In order for astronomers to study gravity in space, they need to make observations of planets and stars with telescopes.

But why do astronomers need to study gravity?

N/A

2-4 mins

Current gravity research

Introduce concept that science research is ongoing and there is still a lot we don’t know.

16

There is still a lot we don’t know about gravity in space. For example, we don’t know if our current theories of gravity are completely correct, or what happens when gravity is very strong, or very weak2.

Looking at the effects of gravity can also tell us about the universe and help us answer questions, such as, “What is Dark Matter?” We need telescopes to look into space to answer these questions (and many more!).

N/A

2 Seven mysteries about gravity: http://www.newscientist.com/special/seven-things-that-dont-make-sense-about-gravity


http://www.newscientist.com/special/seven-things-that-dont-make-sense-about-gravity


4-6 mins

Telescope example

Introduce VLT (Very Large Telescope) as example of current big telescope.

17

Telescopes can be thought of as giant eyes which have been built to collect more light and see objects better.

This is the VLT (Very Large Telescope) and a picture of the Sombrero Galaxy taken by it.

It is owned and run by ESO (the European Southern Observatory). There are 15 countries involved in ESO, including the UK. The VLT is made up of 4 telescopes, each 8 m across. Each telescope uses a curved mirror to collect light and focus it on to a detector. The 4 telescopes can work individually or all together to boost their seeing power.

The VLT is 2.6 km high, on a mountain in Chile where the air is very thin. This means it has an extremely clear view of the sky. It also uses a laser to measure distortions in the air (this is called Adaptive Optics). This means it can take even better quality images3.

For higher achieving pupils, this could be extended into a research task. Pupils could look up this and/or other big telescopes around the world and present their findings to the rest of the class4.

3 More information on the VLT can be found here: http://www.eso.org/public/teles-instr/vlt/4 A list of the ten biggest telescopes in the world can be found here: http://www.space.com/14075-10-biggest-telescopes-earth-comparison.html


http://www.space.com/14075-10-biggest-telescopes-earth-comparison.html

http://www.eso.org/public/teles-instr/vlt/


6-7 mins

Astronomy at other wavelengths

Introduce telescopes that observe other forms of (electro-magnetic) radiation.

18

Light is a form of (electro-magnetic) radiation, but there are many others. Astronomers don’t just use telescopes that look at light, they also use telescopes designed to pick up these other forms of radiation.

Here are three examples: The SOHO (SOlar and Heliospheric Observatory) satellite a joint mission by the European Space Agency and NASA. Launched in 1995, SOHO observes the Sun in light and ultra-violet rays. SOHO is orbiting in space 1.5 million kilometres from Earth5.

NASA’s James Webb space telescope is due for launch in 2018. It will observe cool objects in the universe by detecting infrared radiation. It will look for the first galaxies after the Big Bang and see how stars and planets form in massive clouds of gas and dust6.

The Lovell telescope at Jodrell Bank in Cheshire is part of the University of Manchester. It was built between 1952 and 1957 and it picks up radio waves from objects like exploding stars, dead stars and galaxies out in space. Its dish is 76 metres across, which makes it the third largest steerable telescope in the world7.

Some pupils may be familiar with some other forms of radiation, especially infrared radiation (which can be felt as heat). This is the same radiation that is picked up by heat and night vision cameras.

This content links in to most Key Stage 4 specifications on the electro-magnetic spectrum.

7-8 mins

Example of observations

Example of an observation in another form of radiation.

19 This is an image of the Sun as it appears to our eyes, in visible light (warning: never look directly at the Sun!).

By looking with ultra-violet rays however, we can see many more features that we couldn’t before. This image was taken by the SOHO satellite. By looking with other forms of radiation, astronomers see things that would be completely invisible in ordinary light. Other forms of radiation reveal a hidden universe!

N/A

5 More on SOHO at: http://sohowww.nascom.nasa.gov/6 More on James Webb Space Telescope here: http://jwst.nasa.gov/index.html7 More on the Lovell telescope at: http://www.jb.man.ac.uk/aboutus/lovell/


http://www.jb.man.ac.uk/aboutus/lovell/

http://jwst.nasa.gov/index.html

http://sohowww.nascom.nasa.gov/


8-9 mins

Advantages of big telescopes

List the advantages of big telescopes.

20

Right now scientists and engineers around the world are building new, bigger and better telescopes. Big telescopes see better than smaller ones, but why?

Firstly, big telescopes collect more light, so can see fainter objects (like eyes widening in the dark).

Big telescopes also create better quality (sharper) images8.

Some pupils may be able to predict that big telescopes can collect more light, especially if prompted to consider the eye as an analogy. Pupils could think-pair-share their ideas.

9-10 mins

Example of future telescope

Example of a future science and engineering development.

21

With modern technology (e.g. supercomputers and fibre-optic data networks) it is preferable to build many linked smaller telescopes, rather than single large ones.

The Square Kilometre Array (SKA) will be the largest radio telescope in the world, built of over 3000 smaller dishes, spread across the deserts of Australia and South Africa9. It will act like one giant telescope thousands of kilometres wide. A telescope that size would be impossible to build as one giant dish! The SKA will be so powerful it will be able to detect organic molecules in space.

The SKA is being built by a global partnership of ten countries: Australia, Canada, China, Germany, Italy, New Zealand, South Africa, Sweden, the Netherlands and the United Kingdom (India is also an Associate Member).

N/A

8 The explanation for this is A-level physics, so it is not addressed here, but it can be found at http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/cirapp.html9 More information on SKA can be found at http://www.skatelescope.org/


http://www.skatelescope.org/


Part 3: Gravity in Space

Learning Objectives

All To comprehend the terms star, galaxy and universeMost Use a 3D model of gravity to address the misconception that there is no gravity in spaceSome Evaluate a 3D model of gravity



0-3 mins

Introduce Part 3

Introduce gravity on a larger scale. 22

Now we will consider how gravity acts on larger scales; not only on the surfaces of planets, but further out. Gravity affects how all objects in space move, such as planets and stars.

As a starter: Pupils could guess what the picture on slide 22 shows. Pupils could write their guesses on mini-whiteboards or post-it notes.

The image shows an artist’s impression, using real data from the European VLT telescope, of the stars which orbit the supermassive black-hole at the centre of our Milky Way galaxy and the cloud of gas which is falling into it. It’s the force of gravity from the black-hole that is causing all this to happen.

Some pupils may not yet be familiar with the term galaxy.



3-5 mins

Assess prior knowledge

Assess pupils' understanding of the direction of the force of gravity.

23

Ask pupils which arrow correctly represents the force of gravity acting on the astronaut.

Gravity will act between the centre of the astronaut and the centre of the Earth. Technically, gravity will act equally in both directions, but the effect of the force on the Earth from the astronaut is negligible (since the Earth is so massive) and so it can be ignored. The astronaut will be pulled towards the centre of the Earth.

Pupils could vote on their choices using voting cards, or mini-whiteboards. For higher achieving pupils the options could be deleted and pupils could draw their answer on the board, if using an IWB. Alternatively side 23 could be printed out for pupils, to answer individually or in pairs/groups.

5-15 mins


Introduce practical activity. 24 See section Practical activity 2 for more information about the

practical activity available at this point.

High achieving pupils could be asked to design and construct their own models of gravity.

Pupils use a 3D model of gravity. 25 Slide 25 lists some examples of questions pupils could investigate

using the equipment.

Question 5 (what are the similarities and differences between this model and real life?) is aimed at high achieving pupils (see Practical activity 2 for more information).

15-17 mins

Identify examples in space where gravity acts

Example 1: Satellites

26 Gravity keeps satellites in orbit around the Earth.

A ball tethered to a piece of string and whirled overhead can be used to represent an orbit. The tension in the string represents the tug of gravity; preventing the ball/satellite from hurtling off into space.

High achieving pupils could be asked to come up with a list of examples before being presented with slides 26-28.

Other examples could include; keeping Moons in orbit around planets, the pull of black holes, galaxies interacting with each other, and so on.



17-21 mins

Identify further examples in space where gravity acts

Define terms star and galaxy

Example 2: planets 27

In exactly the same way, gravity keeps planets in orbit around the stars.

It is a common misconception that gravity drives the motion of the planets around the Sun. This is not the case. There is no force driving the planets around the Sun; the planets were formed in motion and there are no resistance forces in space to slow them down.

N/A

Example 3: Galaxies 28

Stars are grouped together in space in galaxies. On average a galaxy contains about 100 billion stars. Stars are held together in galaxies by the force of gravity between them.

This is a picture of galaxy NGC1300, taken by the Hubble Space Telescope. It is a barred spiral galaxy with two spiral arms (barred refers to the straight 'bar' of stars that runs through the central bulge of the galaxy). This is the same type of galaxy that we think our Milky Way galaxy is. We cannot take an image of our own galaxy like this, since we are inside it. Our Milky Way galaxy contains around 200 billion stars.

A popular analogy is that a galaxy is like a 'city' of stars; the stars being the individual houses in that city.

N/A



21-24 mins

Define term universe

Consider image of Hubble Deep Field. 28

This is an image called the Hubble Ultra Deep Field, taken by the Hubble Space Telescope. The Hubble Space Telescope was pointed out into deep space to take this image. The image is of a tiny patch of sky, in which we can see almost to the edge of the observable universe. The image shows many galaxies, separated by vast distances of empty space. It is estimated that there are around 100 billion stars in the observable universe.

The term universe refers to everything; all the matter and energy in existence.

Higher achieving pupils could estimate the number of stars in the observable universe; 100 billion stars per galaxy x 100 billion galaxies = 1024 stars. This number is larger than the total number of grains of sand on all the beaches of the Earth!

24-30 mins

Review of Part 3

Assess whether learning objectives have been met.

29

To assess the learning objectives of part 3, pupils can answer the eight questions presented on slide 29.

See Answers to the Part 3 Review for the answers.

Higher achieving pupils could be asked to review the 3D model of gravity used. That is: in what ways did the model successfully simulate the force of gravity? In what ways did it fail? How could the model be improved?




Objective: To measure the strength of gravity on the Earth's surface.

Option 1: Freefall (Data logging)

The strength of gravity is also defined as the 'acceleration due to gravity'. Therefore it is possible to directly measure the strength of gravity by measuring the acceleration of an object as it drops to the ground. For an experiment of this nature, we recommend a group size of three or four.

If you choose to run a freefall experiment, you may need to consider the following:

You will probably need to use data logging equipment which uses one or two light-gates. Choose suitable objects to drop; smaller, denser objects work best as they are less affected by

air resistance. Also, if using data logging equipment, the objects may need to be a regular size; e.g. square. Please check what your data logging software recommends.

Data logging software will usually enable your pupils to collect a high number of results. However, many of these results may be highly inaccurate, e.g. if the dropped object only falls through one light gate and misses the second, or falls at an awkward angle. To enable pupils to record successful and unsuccessful readings, we have provided a “Data validity worksheet”. By referring to this record when analysing their results, pupils can remove their unsuccessful readings from the calculation of their average.

It may be possible to demonstrate that acceleration due to gravity is independent of the weight of the object being dropped (i.e. heavy objects do not fall quicker than light objects). This depends on pupils collecting good quality results in terms of accuracy. Provide pupils with a variety of objects of different weights, but similar sizes (exactly the same size if possible). For example, small blocks made out of wood or metal. Provided the lightest objects are not so light that they are greatly affected by air resistance, there should not be a correlation between weight and acceleration.

Depending on the equipment available in your school, it is possible to run a freefall experiment with one or two light-gates. See more information on these options below.

A. Using data logging equipment with two connected light-gates

Equipment neededComputer/laptop running data logging software

A pair of connected light-gatesClamp-stand

Regular shaped object to drop

The easiest way to complete a free-fall experiment is with data logging equipment that uses two connected light-gates. Attach the light-gates to a clamp stand, one on top of the other, and then drop an object through the light gates, making sure the object breaks the beams of both light gates. Most data logging software will directly calculate the acceleration of the object, provided the size of



the object and the distance between the light-gates is known. Please refer to your data logging software instructions on how to do this. Pupils can then copy their results to an Excel spreadsheet, where they can delete unsuccessful readings and/or anomalous data before calculating their average.

B. Using data logging equipment with a single light gate

If you do not have access to connected pairs of light-gates, another option is to use a single light-gate and a stopwatch.

Equipment neededComputer/laptop running data logging software

A light-gateClamp-standStopwatch

Regular shaped object to drop

Drop an object from a suitable height above the light-gate. Time on a stopwatch how long it takes from the start of the drop, to the object passing through the light-gate. The height of the drop does not need to be known. The light-gate should be used to take a measurement of the final speed of the object. Most data logging software will directly calculate the speed, provided the size of the object is known. The acceleration can then be calculated from the equation acceleration = (final speed - initial speed) ÷ time. Since the initial speed = zero (provided the object is dropped, not thrown), this simplifies to acceleration = final speed ÷ time. Pupils could enter their results into an Excel spreadsheet which calculates the acceleration for them, using this equation. Pupils can also delete unsuccessful readings and/or anomalous data before calculating their average.

Option 2: Newton meters

If light-gates and data loggers are not available to you, pupils can measure the strength of gravity on Earth by taking measurements from masses hanging from Newton meters.

Equipment neededNewton meter

Variety of masses

By hanging different masses from Newton meters and reading off the weight, it is possible to calculate the strength of gravity in N/Kg, from the equation strength of gravity = weight ÷ mass. Pupils may get a variety of readings from different Newton meters and also if the masses attached are too low to stretch the spring, or so large that they overstretch the spring. This will give pupils the opportunity to identify anomalous results and to calculate a class average. For a Newton meter experiment, we recommend a group size of two.



Practical Activity 2

Objective: To use a 3D model of gravity to address the misconception that there is no gravity in space.

MethodEquipment needed

Hula hoopApprox 1m2 (depends on size of hula hoop) of stretchy lycra material

Bulldog clipsBalls of different sizes and masses

Cut a section of stretchy lycra material so that it can be stretched taut over a hula hoop and securely clip it with bulldog clips around the edge. This is now a 2D representation of space. Hold up the hula hoop above the ground and place a ball on the lycra surface. A suitably heavy ball will sink into the lycra, creating a curve. The ball represents a star or planet in space and the curved lycra represents the gravity field around it.

Pupils should draw an analogy between the stretched lycra and an object’s gravity extending outwards into space, gradually getting weaker as the distance increases. This will hopefully work towards dispelling the misconception that gravity is binary, i.e. that is that it is ‘on’ at the surface of the Earth and ‘off’ when in space.

This model actually represents the curved ‘spacetime’ of Einstein's theory of General Relativity, published in 1916. In this theory, Einstein proposed that mass bends spacetime around it, curving and stretching space and time (opposed to the perfectly flat space in classical physics). Objects, e.g. planets or particles or rays of light, travelling near massive objects such as stars and other planets follow the curvature of space, so their path bends around these objects. We perceive this change of direction as the force of gravity pulling on them.

For this activity, we recommend a group size of three or four. An excellent (if very large scale!) demonstration of this activity can be found at: https://www.youtube.com/watch?v=MTY1Kje0yLg.

Examples of things to tryThese are listed on slide 25 of the accompanying PowerPoint, but more information is found below.

1. Place a second ball onto the lycra. The two balls will be attracted together, if they come too close to one another.

2. Experiment with the strength of the 'gravity fields' around balls of different masses.3. Try to get a planet (a smaller, lighter ball, e.g. a marble) to orbit around a star (a larger,

heavier ball).a) By rolling the planet around the star. It’s possible to get one or two good orbits, but not

many more; the planet will lose energy quickly and start spiralling into the star, due to the friction of the fabric (there is no friction in space, so this does not occur).

b) By applying small rotations. First, apply a bit of pressure to the star to hold it in place. Now those holding the hula hoop can rotate it in small circles. This will provide the force


https://www.youtube.com/watch?v=MTY1Kje0yLg


necessary to overcome the friction of the lycra and start the planet rolling around (in real space there is no friction, so no constant driving force is required). The gravity of the star will constrain the planet and keep it in orbit. If the driving force is too strong, the planet will overcome gravity and fly off out into space.

4. Try to get a planet to orbit two stars in a figure of eight shape (you may have to hold the stars in place to stop them attracting together). Many stars exist in binary systems. A figure of eight also represents the path the Apollo missions took to get to and from the Moon.

5. Consider the similarities and differences of this model with real life (for higher achieving pupils). This model excellently demonstrates the pull of gravity in one plane, however in reality gravity acts in three dimensions. Also this model has a lot of friction, so objects lose energy quickly.



Answers to the Mass and Weight worksheet

1. How much would a 10 Kg suitcase weigh on the surface of…?a. The Moon 16 Nb. Mars 37 Nc. Saturn 90 Nd. Pluto 6 N

2. How much would a 25 Kg suitcase weigh on the surface of…?a. Mercury 95 Nb. Venus 220 Nc. Jupiter 577.5 Nd. Uranus 217.5 N

3. What would be the mass of a 10 Kg suitcase be on…?a. Mercury 10 Kgb. Venus 10 Kgc. Neptune 10 Kg

4. Which place in the above table will it be easiest to stand up? Why? Pluto, gravity is weakest5. On which place from the table above would you have…?

a. The most weight Jupiterb. The most mass N/A: mass would be the same on every one

6. If you stood on Mars and had to pick up a 15 Kg pack, you would have to pull with a force greater than…? 55.5 N (this is the force of weight on the pack)

7. If a 60 Kg person was standing on a platform at the surface of Saturn and they jumped, they would have to push with a force greater than…?

540 N (this is the force of weight on the person)8. The Curiosity rover on Mars has a weight on Mars of 3,330 N. What is its mass?

mass = weight/g = 3330/3.7 = 900 Kg9. A 60 Kg person standing on the dwarf planet Ceres would weigh 16.2 N. What is the strength

of gravity on the surface of Ceres? g = weight/mass = 0.27 N/Kg10. Jupiter is made of gas (like Saturn, Uranus and Neptune). What would happen to the

strength of gravity if you...?a. Moved away from Jupiter It would get weakerb. Fell in to Jupiter It would get stronger



Answers to the Part 1 Review

1. What is mass and what is it measured in?Mass is a measure of the amount of matter that an object is made of.It is measured in Kilograms.

2. What is weight and what is it measured in?Weight is the amount of force acting on an object with mass, due to gravity.It is measured in Newtons.

3. Write down the equation that relates mass and weight.Weight = Mass x gravity

4. What is an anomalous result and why should you ignore it?An anomalous result is one that is very obviously different from other measurements, due to some error in the experiment. It should be ignored to give more accurate results.

For questions 5 and 6, imagine both objects being dropped at the same time and from the same height.

5. A bowling ball and a leaf.a) Which object would land first on the Earth? Bowling ballb) Which object would land first on the Moon? Both would land at the same timec) Which object weighs more? Bowling ball

6. A piece of paper scrunched up into a ball and an identical, but flat piece of paper. a) Which object would land first on the Earth? Scrunched up paperb) Which object would land first on the Moon? Both would land at the same timec) Which object weighs more? Both weigh the same

Answers to the Part 3 Review

1. Place these objects in order from smallest to largest: Galaxy, universe, planet, star.Planet, star, galaxy, universe

Decide whether the statements are true or false. If the statement is false, write a correct statement.2. The Earth’s gravity pulls objects downwards, towards the South pole.

FALSE. Gravity pulls objects towards the centre.3. There is no gravity in space.

FALSE. Gravity extends outwards into space from objects.4. The more mass an object has, the stronger its force of gravity. TRUE.5. A planet’s gravity pulls objects towards the centre of that planet.. TRUE.6. The force of gravity extends outwards from objects. TRUE.7. Gravity sometimes pushes objects apart.

FALSE. Gravity only attracts objects together.8. The force of gravity from an object stays the same no matter how far away you are from the

object.FALSE. The force of gravity gets weaker the further you go from an object.



Additional resources on big telescopes

1. Full 50 minute documentary about current big optical telescopes http://www.youtube.com/watch?v=QeobrudynUE

2. Square Kilometre Array Official Animations http://www.skatelescope.org/media-outreach/videos/

3. More information about current and future big telescopes, including school resources http://www.bigtelescopes.org.uk/

4. Star Gazing Live video demonstrating how to make your own small telescope http://www.bbc.co.uk/programmes/p00n6zkf

Use of Images

All images used in this lesson's presentation have been released under a creative commons license. Every effort has been made to credit all images used. Where images do not display credits, this is because this information could not be found. If you believe an image has been used incorrectly or has been mis-credited, please email Jamie Sloan on the address shown below and we will be happy to amend the [email protected]


http://www.bbc.co.uk/programmes/p00n6zkf

http://www.bigtelescopes.org.uk/

http://www.skatelescope.org/media-outreach/videos/

http://www.youtube.com/watch?v=QeobrudynUE

Gravity: Lesson Plans

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Transcript of Gravity: Lesson Plans