Improvements Needs reordered according to gravity notes for real. Look up common misconceptions &...

Improvements

• Needs reordered according to gravity notes for real.

• Look up common misconceptions & address them

Today you are going to…take notes on gravity!

So you can…

You’ll know you’ve got it when you can • Accurately answer the questions

Bell Work 4/8/13

New Bell Work Sheet!

1. How many Newtons would a 885.0 kg object weigh on Earth’s surface? (Use F = ma, a = 9.81 m/s2)

2. Convert this to lbs.

The 4 Fundamental Forces

Gravity!

• What does it do?– Makes objects fall– Keeps objects on Earth– Keeps objects in orbit!

Gravity!

• Gravity is the attraction between any two objects that have mass.

• It’s actually the weakest force!

• It’s magic!!– We don’t really understand it (but then, that’s

true of most fundamental stuff)

• Sir Issac Newton wrote the law of universal gravitation.

• Universal gravitation equation G =

• The force of gravity is ___________________ related to mass.

• The force of gravity is ___________________ related to distance.

• 2 things affect the force of gravity: ___________ and _____________

The Law of Universal Gravitation!

What happens to the force of gravity if the mass doubles? If the distance doubles? So gravity depends more on ___.

• Gravity is the attraction between any two objects that have mass. Why don’t we notice the force of gravity between all objects?

• Would your mass or weight be any different on the moon? Why?

• Would your mass or weight be any different on the top of a tall mountain? Why?

Magnets!

• The force of magnetism

• Which is stronger, gravity or magnetism?

• How are gravity and magnetism similar?

• How are gravity and magnetism different?

Freefall!

• An object is in freefall when gravity is the only force acting on it.

• All things on Earth’s surface fall with same acceleration (_______). This means if they were both dropped from the same height, they would hit the ground at the same time. Why don’t we notice this?

• Strobe light & drops of water!

The Law of Universal Gravitation!

What all is the same on the surface of Earth? Figure out that everything else must be equal to acceleration due to gravity.

Air Resistance!

• Air resistance keeps all objects from falling with the same acceleration on Earth.

• Terminal velocity – the fastest an object can fall due to air resistance– Happens when force of air resistance = weight

• FNET = 0, therefore a = _______!

• Moon Hammer Drop

• Feather in vacuum

• Elephant and feather on physics classroom

Freefall! • Why do all things fall with the same

acceleration? Shouldn’t heavier objects fall faster?

• What do we call Earth’s force of gravity on an object?

• On the surface of Earth, 1.0 kg weighs about 9.81 Newtons. A 5.0 kg object weighs 44.05 Newtons. Calculate its acceleration when dropped.

• A 10.0 kg object weighs 98.1 Newtons. Calculate its acceleration.

Why is the acceleration for everything the same?

• If something has twice the weight, it also has twice the inertia, therefore it’s twice as hard to accelerate.

• Gravity is like horse drawn carriages, or a bunch of tiny magnets!

• Would two pieces of clay fall faster if combined?

Bell Work

• Which falls faster, a bullet that’s fired or a bullet that’s dropped?

Today you are going to…take notes on projectiles, circular motion, and weightlessness.

So you can…

You’ll know you’ve got it when you can • Accurately answer the questions

Schedule Monday Gravity Notes & Questions

Tuesday

Projectile & Circular Motion Notes & Questions

WednesdayOrbits!

ThursdayReview Questions & Begin Egg Drop Project

Friday

Build Egg Drop Project

Projectile Motion

Projectile Motion

• Projectile motion - curved path objects follow when projected (thrown, shot, launched, etc.) near surface of Earth– Ex. Thrown football, bullet shot, cow launched

from catapult.

• Projectiles follow curved path called a parabola.

Projectile Motion

• Projectiles are in freefall!

• On Earth, 2 forces act on objects in projectile motion. – gravity and air resistance.

• Air resistance is usually ignored.

Vertical Projectile Motion

• When you throw something straight up into the air:– It takes as long to go up as it does to come down

to the same point at which you released it. – It will be going the same speed in the opposite

direction when it reaches its original height.– At its maximum height:

• v = • t =

Projectile Motion• has horizontal (left & right) & vertical (up & down)

motion. • The horizontal and vertical motion are

independent. – They don’t affect each other!

• Which will hit the ground first, a bullet fired from a gun or a bullet dropped from the same height?

• Mythbusters!!• http://www.youtube.com/watch?v=D9wQVIEdKh8

Projectile Motion• What 2 things affect the distance of a

projectile?

• What angle will launch a projectile farthest?

• What angles will launch projectiles the same distance?

Projectile Motion

Shoot a Monkey!

• http://www.youtube.com/watch?v=cxvsHNRXLjw

• Can an object be moving upwards if nothing is pushing it?

• Can an object be moving horizontally if nothing is pushing it?

• Is force required to keep an object in motion? (Newton’s ______ Law)

Weight

Weight Weight don’t tell me!• Weight - force of gravity between objects & a

planet.

• Mass measures: – how much matter something has– How much inertia something has

• (how hard it is to accelerate)

• 1 kg (mass) weighs 9.8 N = 2.2 lbs

• 1 N = 0.224 lbs (about ¼ lb)

• 1 lb (weight) = 4.46 N

• F = ma

• Fweight = ma

• a = 9.81 m/s2 on Earth’s surface

• What is the weight of a 2.0 kg object?

• What is the weight of a 9.0 kg object?

Bell Work

• Which direction do you think the doughnut will travel when the string breaks?

Today you are going to…take notes on circular motion.

So you can…understand the direction of acceleration & velocity in circular motion and “centrifugal” force.

You’ll know you’ve got it when you can • Accurately answer the circular motion questions.

Circular Motion

Circular Motion

• Objects in circular motion are accelerating towards the center

• Centripetal force – force acting on an object in circular motion; pulls towards center of circle

Circular Motion

• Shape of horizontally thrown projectile

Centripetal Force• Force diagram of object in circular motion

The forbidden F word!

• Centrifugal force – imaginary center fleeing force on an object in circular motion

• NOT REAL

• Caused by inertia…the object wants to keep traveling in a straight line

Car driving in circles

The forbidden F word!

• Circular motion demos

• Why does it stay there? (a law)

• What force acts on it? What direction?

Demos & PuzzlesWhat provides the force • Tom’s puzzle• Penny in balloon• Marble & tape• Ball on string• Color changing ball

• Ball on string through tube with weight

• Question: A ball is being whirled around by a string. If the string suddenly breaks (or is let go), what direction will the ball travel; A, B, C, or D? (Neglect gravity) HAMMER THROW!!!

Doughnut on a string!

• http://www.youtube.com/watch?v=TniQtoapVrQ&feature=related

• Answer: Path ___

• While attached to the string, the ball is forced to follow a curved path. But once the string is gone, no force is exerted and (law of inertia) it follows a straight-line path.

Today you are going to…take notes on orbits!

So you can…understand how satellites, moons, and planets orbit things.

You’ll know you’ve got it when you can • Accurately answer the questions.

Projectile Motion & Orbits


• Force diagram of object in circular motion– (this should be earlier in slide show, when

circular motion first mentioned)


• Objects orbiting Earth are in free fall!– They’re falling!– Gravity acts as the centripetal force– Cannonball!

Satellites!

Earth satellite - projectile moving fast enough to fall continually around Earth rather than into it.

Why can’t we put a satellite into orbit at low altitudes on Earth?

Earth Satellites

In the curvature of Earth, the surface drops a vertical distance of nearly 5 meters for every 8000 meters tangent to its surface.

Earth Satellites

A satellite in circular orbit close to Earth moves tangentially at 8 km/s (5 mi/s). During each second, it falls 5 m.

• Orbital speed for close orbit about Earth is 8 km/s or 29,000 km/h (18,000 mi/h).

•At that speed, atmospheric friction would burn an object to a crisp.

•A satellite must stay 150 kilometers (94 miles) or more above Earth’s surface—to keep from burning due to the friction.

For a satellite close to Earth, the time for a complete orbit around Earth, its period, is about 90 minutes.

Earth Satellites

To escape Earth’s gravity, an projectile must be launched at a velocity of 11.186 km/s = 25,000 mph.

Rockets aren’t projectiles…they don’t need to go this fast.

Pioneer 10, launched from Earth in 1972, escaped from the solar system in 1984 and is wandering in interstellar space.

Escape Velocity

Space Junk!

Bell Work 4/8/11 – 4 minutes1. Convert the following weight to Newtons.

A. 16 lb bowling ball Find the mass of the above in kilograms.

2. Explain how satellites orbit Earth.

Weightlessness!

Circular Motion & Gravitation 65

Weight & Weightlessness• How would it feel to be weightless?

• How do you feel your weight?


Weight & Weightlessness• What you feel as your “weight” is a

sensation due to the normal force

• Just because you don’t feel your weight, doesn’t mean you’re weightless!

• Astronauts in space are not really weightless.


Weight & Weightlessness• Astronauts are just in constant freefall!

• Since there’s nothing holding them up, they feel weightless!

Would you like to be weightless?

Zero-G

• People On Vomit Comet

• http://www.youtube.com/watch?v=N6ZJnIJRUCI&feature=related

• Water balloons in zero gravity http://www.youtube.com/watch?NR=1&feature=fvwp&v=gTqLQO3L4Ko

Bell Work 4/11/12

1. What is a satellite?

2. What are the forces acting on a satellite?

3. How long does it take a satellite to orbit Earth?

4. Can we see satellites with the naked eye?

5. How fast do you have to throw a ball to throw it off of the planet?

• Pluto has a mass of 1125 x 1022 kg and an equatorial radius of 1195 km. (a) Calculate the acceleration due to gravity on the surface of Pluto. (b) A python weighs 980 N on Earth. How much would it weigh on Pluto?

MP = 1024 kgrP = 1195 km = 1195000 m = 1.195 x 106 m G = 6.67 x 10-11 N m2/kg2

g = G MP/rP2

g = (6.67 x 10-11)(1024)/(1.195 x 106 )2

g = 4.78 x 10-20 m/s2

WE = 980 NgE = 9.8 m/s2

gP = 0.59 m/s2

WP = ? N

WE = mgE

980 = m(9.8) 100 kg = m

W = mg = (100)(4.78 x 10-18m/s2) = 4.78 x 10-18 N

• The elephant and the feather each have the same force of gravity.• The elephant has more mass, yet both elephant and feather

experience the same force of gravity.• The elephant experiences a greater force of gravity, yet both the

elephant and the feather have the same mass.• On earth, all objects (whether an elephant or a feather) have the

same force of gravity.• The elephant weighs more than the feather, yet they each have the

same mass.• The elephant clearly has more mass than the feather, yet they each

weigh the same.• The elephant clearly has more mass than the feather, yet the

amount of gravity (force) is the same for each.• The elephant has the greatest acceleration, yet the amount of

gravity is the same for each.

Bell Work 4/8/11 – 5 minutes1. Convert the following weights to Newtons.

A. 16 lb bowling ball B. 17 lb cat

C. 20,000 lb truck

2. Find the mass of the above in kilograms.

3. If an object has reached terminal velocity, what is the net force on the object? What’s its acceleration?

4. T/F An object in orbit is actually falling.

Bell Work 4/4/11 – 5 minutes

START NEW MONDAY BELL RINGER FOR 4TH QUARTER

1. Define mass according to chemistry and according to physics.

2. W5SAYW

Bell Work 3/30/12 – 5 min

1. Robbie can throw a 3.0 kg medicine ball with an acceleration of 10.0 m/s2. What acceleration could he give a 9.0 kg medicine ball? Show your work!

2. If you were in a plane, would your weight or mass change? Why?

The moon has a radius of 1.74 million meters and a mass of 7.32x1022 kg. In both MKS and FPS units, determine the acceleration due to gravity on the lunar surface.

M = 7.32 x 1022 kg r = 1,740,000 m = 1.74 x 106 m a = ?

a = GM r2 a = (6.67 x 10-11)(7.32 x 1022 kg ) (1.74 x 106)2

48.824 x 1011

3.02 x 1012

16.17 x 10-1

1.62 m/s2

Bell Work 4/11/11 – 5 minutesMass (kg) Weight on Earth

Newtons Pounds

1. 1 kg ____N ____lbs

2. 50 kg ____N ____lbs

3. 0.102 kg ____N ____lbs

4. _____ kg 500 N ____lbs

5. _____ kg 50 N ____lbs

6. _____ kg ____N 2,000 lbs

7. W5SAYW

Bell Work 3/29/12 – 5 min1. A force of 250.0 lbs acts on an object with a

mass of 8.0 kg. What’s it’s acceleration?

2. What is gravity?

Bell Ringer 4/1/11 – 2 min

1. If the mass of an object magically doubled, the force of gravity between it and other objects __________.

2. If the distance between two objects doubles, the force of gravity between them is ____ what it was.

Bell Work 4/7/11 – 5 minutesUse the conversions between lbs, kg, and N in your notes to answer

the following questions.

1. What is the difference between mass and weight? Give 2 units that measure weight and 1 unit that measures mass.

2. Change the following weights to Newtons. 12 lb bowling ball 117 lb teen 1600 lb car

3. Find the weight of the following masses in Newtons AND pounds.

1 kg 5 kg 1000 kg

If Pandora has a mass of 5.00 x 1024 kg and a radius of

6.00 x 103 km, find the weight of a 110 kg Na’vi on Pandora’s surface. (Pay attention to the units!)

MP = 5.00 x 1024 kg mN = 110 kg r = 6.00 x 103 km = 6.00 x 106 m W = Fg =?

Fg = GMPm r2 Fg = (6.67 x 10-11)(5.00 x 1024 kg )(110 kg)

(6.00 x 106)2

Fg = 1019 N

Tips for using the G equation.

• Make sure you square r!

• You’ll be dealing with big numbers…don’t forget the exponents! “x 10-11”!

• Double check your answers.

Satellite Motion

1. What is a satellite?

2. What are the forces acting on a satellite?

3. How long does it take a satellite to orbit Earth?

4. Can we see them with the naked eye?

5. How fast do you have to travel to get escape this planet?

The speeds of the bowling ball and the satellite are not affected by the force of gravity because there is no horizontal component of gravitational force.

14.2 Circular Orbits

The satellite is always moving at a right angle (perpendicular) to the force of gravity.

• It doesn’t move in the direction of gravity, which would increase its speed.

• It doesn’t move in a direction against gravity, which would decrease its speed.

• No change in speed occurs—only a change in direction.


For a satellite in circular orbit, no force acts along the direction of motion. The speed, and thus the KE, cannot change. What force or forces hold satellites in orbit?

14.4 Energy Conservation and Satellite Motion

A satellite in circular orbit close to Earth moves tangentially at 8 km/s (5 mi/s). During each second, it falls 5 m beneath each successive 8-km tangent.

What happens to the velocity of a satellite as the distance from Earth increases?


Improvements Needs reordered according to gravity notes for real. Look up common misconceptions &...

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