Newton’s Laws of Motion and Newton’s Laws of Motion and Universal ForcesUniversal Forces

Unit 1

Physical Science HS Credit

Mrs. Rubel

Newton’s Laws of MotionNewton’s Laws of Motion

Begins Here!!Begins Here!!

Great ScientistsGreat Scientists Aristotle- Incorrectly said Aristotle- Incorrectly said

force was required to keep an force was required to keep an object in constant motionobject in constant motion

Galileo- with no resistance Galileo- with no resistance objects would move objects would move indefinitelyindefinitely

Newton- based on Galileo’s Newton- based on Galileo’s findings he came up with his findings he came up with his law’s of motionlaw’s of motion

Newton’s 1Newton’s 1stst Law of Motion Law of Motion AKA The Law of Inertia AKA The Law of Inertia

Inertia-Inertia- an objects tendency to resist an objects tendency to resist

changes in motionchanges in motion an object at rest will remain at rest, and an object in motion will remain in an object at rest will remain at rest, and an object in motion will remain in

motion in the same direction at a constant velocity until acted on by another motion in the same direction at a constant velocity until acted on by another force.force.

Remember: The greater the mass of an object the greater the inertia

Have you heard of the FORCE of gravity?Have you heard of the FORCE of gravity? Gravity: the force that pulls objects towards each otherGravity: the force that pulls objects towards each other Since gravity is a force it also obeys Since gravity is a force it also obeys Newton’s second lawNewton’s second law

F=maF=ma

With this experiment, Galileo proved Aristotle wrong

Since objects fall at the same

speed, their acceleration is

the same.All objects

accelerate at the rate. Here on Earth the

rate is: Ag=9.8 m/s2

OrAg=32 ft/s2

With this experiment, Apollo 15 astronauts proved Galileo right.(link to You Tube)

Weight and MassWeight and Mass

Weight is the force of gravity acting on an objectWeight is the force of gravity acting on an object Weight (N) = mass (g) x acceleration of gravity (m/sWeight (N) = mass (g) x acceleration of gravity (m/s22)) Note: just a version of F=ma, F = mass x gravity Note: just a version of F=ma, F = mass x gravity

FYI:FYI: 1 pound = 4.448 Newtons1 pound = 4.448 Newtons so 1/4 lb is slightly more that 1 Nso 1/4 lb is slightly more that 1 N so a 1/4 lb burger is a "Newton" burgerso a 1/4 lb burger is a "Newton" burger

F=maF=ma So, So, weight is a type of Forceweight is a type of Force The formula for weight: The formula for weight: Weight = mass x AWeight = mass x Agg

SinceSince A Agg= 9.8 m/s= 9.8 m/s2 2 then then

Weight = mass x 9.8 m/sWeight = mass x 9.8 m/s22

Newton’s 2Newton’s 2ndnd Law & Weight Law & Weight

Remember:1 newton = 0.22 pounds

Try This:

A bicycle takes 8.0 seconds to accelerate at a constant rate from rest to a speed of 4.0 m/s. If the mass of the bicycle and rider together is 85 kg, what is the net force acting on the bicycle? (Hint: First calculate the acceleration.)

For every action there is an equal & opposite reaction.For every action there is an equal & opposite reaction.

This means every time a force is applied in This means every time a force is applied in one directionone direction an an equal forceequal force is applied in the is applied in the opposite direction.opposite direction. If an object is not in motion, then all forces acting on it are balanced and the net force is zero!If an object is not in motion, then all forces acting on it are balanced and the net force is zero!

Newton’s 3Newton’s 3rdrd Law of Motion Law of Motion::

Action-Reaction ForcesAction-Reaction Forces

If you push against a If you push against a wall it pushes backwall it pushes back

These forces can cause These forces can cause motion, like a swimmermotion, like a swimmer

They do not cancel They do not cancel each other out, because each other out, because they act on different they act on different objects.objects.

2 ice skaters2 ice skaters

Questions that make you go Questions that make you go Hmmmmmmm….Hmmmmmmm…. 11. Why can you exert greater force on the pedals of a bicycle if you . Why can you exert greater force on the pedals of a bicycle if you

pull up on the handlebars?pull up on the handlebars? When you pull up on the handlebars, the handlebars push down When you pull up on the handlebars, the handlebars push down

on you, and this force is transmitted to the pedals.on you, and this force is transmitted to the pedals. 2. Lets say you are weighing yourself on a set of bathroom scales. 2. Lets say you are weighing yourself on a set of bathroom scales.

You are standing next to the sink in the bathroom. If at the same time You are standing next to the sink in the bathroom. If at the same time while you are standing on the scales you reach under the sink and while you are standing on the scales you reach under the sink and pull up on the sink, will the scales register your weight to be more or pull up on the sink, will the scales register your weight to be more or less than what they would register if you didn't pull up on the sink?less than what they would register if you didn't pull up on the sink? the scales would register heavy. Since you are lifting up on the the scales would register heavy. Since you are lifting up on the

sink, the sink is pushing down on you with an equal but sink, the sink is pushing down on you with an equal but opposite force and this would be transmitted to the scales. opposite force and this would be transmitted to the scales.

Hmmmmmm….Hmmmmmm….

3. Lets repeat the question in the situation above 3. Lets repeat the question in the situation above except that you push down on the top of the sink except that you push down on the top of the sink instead of pulling up on the bottom of the sink. instead of pulling up on the bottom of the sink. What will your weight be this time compared to What will your weight be this time compared to what it would be if you did not push down on the what it would be if you did not push down on the sink?sink? The scales would register lighter. Since you are The scales would register lighter. Since you are

pushing down on the sink it is pushing up on you pushing down on the sink it is pushing up on you with an equal force which tends to lift you up off the with an equal force which tends to lift you up off the scales some and therefore they register light.scales some and therefore they register light.

By definition, a By definition, a ForceForce is a is a pushpush or a or a pullpull..

Just like Velocity & Acceleration Forces have

both magnitude and direction

components

Just like Velocity & Acceleration Forces have

both magnitude and direction

components

Natural ForcesThere are 3 large natural forces that exist on Earth:

1)Gravity

2)Friction

3)Air Resistance

ForcesForces A force causes an A force causes an

object to move, object to move, accelerate, change accelerate, change speed, or directionspeed, or direction

Forces are Forces are represented by:represented by: ArrowsArrows Direction Direction StrengthStrength

represented by the represented by the length of the arrowlength of the arrow

Balanced & Balanced & Unbalanced ForcesUnbalanced Forces

Balanced forces – opposite and equal forces acting on the same object

result in NO motion of the object

Unbalanced forces Unbalanced forces – – two or more forces of two or more forces of unequal strength or unequal strength or direction acting upon direction acting upon on an objecton an object results in motion of results in motion of

the objectthe object

Balanced or Unbalanced Forces?Balanced or Unbalanced Forces?

balanced unbalanced

Force/Free body diagrams Force/Free body diagrams (to show forces)(to show forces) used to show the relative magnitude and used to show the relative magnitude and

direction of all forces acting upon an object direction of all forces acting upon an object in a given situation. in a given situation.

a special example of vector diagrama special example of vector diagram size of the arrow represents size of the arrow represents

amount of forceamount of force

Force / Free-body DiagramsForce / Free-body Diagrams

direction of the arrow shows the direction which the force direction of the arrow shows the direction which the force is actingis acting

each force arrow is labeled each force arrow is labeled The object is usually represented by a box. Force arrows The object is usually represented by a box. Force arrows

are drawn from the center of the box outward in the are drawn from the center of the box outward in the direction which the force is acting.direction which the force is acting.

http://www.physicsclassroom.com/Class/newtlaws/u2l2c.cfm#1 (look at types of forces also) (look at types of forces also)

Combining ForcesCombining Forces Net force: All forces Net force: All forces

are added or are added or subtracted to create subtracted to create one total forceone total force

If net force is Zero If net force is Zero then there is no then there is no change in motion.change in motion.

If there is a net force If there is a net force there is an there is an accelerationacceleration

Force ProblemForce Problem

What is the net force on an object being What is the net force on an object being pulled toward the west with a force of 30N pulled toward the west with a force of 30N and another force pulling the object toward and another force pulling the object toward the east with a force of 75N? the east with a force of 75N?

FrictionFriction

All moving objects All moving objects encounter frictionencounter friction

Without it most Without it most motion would be motion would be impossibleimpossible

4 types, static, 4 types, static, sliding, rolling, fluidsliding, rolling, fluid

Static FrictionStatic Friction

The force that keeps an object from The force that keeps an object from movingmoving

It is the largest frictional forceIt is the largest frictional force Always opposite direction of the applied Always opposite direction of the applied

forceforce Pushing a CarPushing a Car WalkingWalking

Sliding FrictionSliding Friction

Once the object is in motion it experiences Once the object is in motion it experiences sliding frictionsliding friction

Opposite direction from applied forceOpposite direction from applied force Less than static friction so less force is Less than static friction so less force is

needed to keep it in motionneeded to keep it in motion

Rolling FrictionRolling Friction As something rolls, the As something rolls, the

object and floor bend object and floor bend slightly. This bend causes slightly. This bend causes rolling frictionrolling friction

It is a much smaller force It is a much smaller force than static frictionthan static friction As much as 1000 times As much as 1000 times

smallersmaller Allows you to move heavy Allows you to move heavy

objectsobjects Ball bearings reduce frictionBall bearings reduce friction

Fluid FrictionFluid Friction

It opposes the motion It opposes the motion in the liquid or gasin the liquid or gas

Like swimming, it is Like swimming, it is hard to movehard to move

If you are in the air, If you are in the air, fluid friction is called fluid friction is called

air resistanceair resistance At higher speeds it is At higher speeds it is

very noticeable.very noticeable.

Force of GravityForce of Gravity A force that acts between 2 objectsA force that acts between 2 objects an attractive force, pulls objects togetheran attractive force, pulls objects together causes objects to accelerate downwardcauses objects to accelerate downward Falling objects, gravity pulls down, Falling objects, gravity pulls down,

What pushes up?What pushes up? air resistance acts in opposite air resistance acts in opposite

directiondirection Terminal VelocityTerminal Velocity- - when Gravity and when Gravity and

air resistance cancel each other out air resistance cancel each other out (velocity of falling body becomes (velocity of falling body becomes constant)constant)

Terminal VelocityTerminal Velocity

Free Fall – Gravity Only Skydivers say they are in free fall, but that isn’t

true. The only way to have free fall is when gravity is the only force working on you (no air resistance.) You can have free fall in a vacuum.

Here’s the only example of a human being experiencing free fall to the Earth:

 

Projectile MotionProjectile Motion When an object not only goes up and down butWhen an object not only goes up and down but

It is a It is a

Air resistance and gravity are the only forces Air resistance and gravity are the only forces acting on a projectileacting on a projectile

What falls faster, an object that falls straight What falls faster, an object that falls straight down, or one that has a horizontal velocity?down, or one that has a horizontal velocity?

Forces ProblemsForces Problems 1.Two tugboats are moving a barge. Tugboat A 1.Two tugboats are moving a barge. Tugboat A

exerts a force of 3000 newtons on the barge. exerts a force of 3000 newtons on the barge. Tugboat B exerts a force of 5000 newtons in the Tugboat B exerts a force of 5000 newtons in the same direction. What is the combined force on same direction. What is the combined force on the barge? the barge?

2.Draw arrows showing the individual and 2.Draw arrows showing the individual and combined forces of the tugboats in #1. combined forces of the tugboats in #1.

Force ProblemsForce Problems

3.Now suppose that Tugboat A exerts a force 3.Now suppose that Tugboat A exerts a force of 2000 newtons on the barge and Tugboat B of 2000 newtons on the barge and Tugboat B exerts a force of 4000 newtons in the opposite exerts a force of 4000 newtons in the opposite direction. What is the net force on the barge? direction. What is the net force on the barge?

4.Draw arrows showing the individual and 4.Draw arrows showing the individual and combined forces of the tugboats in #3. combined forces of the tugboats in #3.

Force ProblemForce Problem 5.Could there ever be a case when Tugboat A 5.Could there ever be a case when Tugboat A

and Tugboat B are both exerting a force on and Tugboat B are both exerting a force on the barge but the barge doesn't move? Draw the barge but the barge doesn't move? Draw arrows showing the individual and combined arrows showing the individual and combined forces in such a situation. forces in such a situation.

Universal ForcesUniversal Forces

Forces that can be found anywhere Forces that can be found anywhere in the universe in the universe

Electromagnetic ForceElectromagnetic Force Electric and Magnetic Electric and Magnetic

Forces are the only forces Forces are the only forces that can both attract and that can both attract and repelrepel

Electric forces- between Electric forces- between charged particle, positive charged particle, positive attracted to negativeattracted to negative

Clothes in a dryerClothes in a dryer Magnetic forces- N and S Magnetic forces- N and S

poles, opposites attract, poles, opposites attract, likes repellikes repel

Nuclear ForcesNuclear Forces Two forces a strong and a Two forces a strong and a

weak force hold an atom weak force hold an atom togethertogether

The strong nuclear force The strong nuclear force overcomes the protons overcomes the protons repulsion forcerepulsion force

This force is over 100x This force is over 100x stronger than electric stronger than electric forcesforces

The weak force is involved The weak force is involved in radioactive processesin radioactive processes

Fusion vs Fission(see page 113) In nuclear fission, a small amount of mass is

converted into large amounts of energy. The nuclei of atoms are broken apart. Nuclear power plants used this energy to generate electrical energy.

In nuclear fusion, a small amount of mass becomes much larger when nuclei of atoms combine. An example would be the Sun, when hydrogen atoms combine to become larger helium atoms.

Gravitational ForceGravitational Force Attractive force between Attractive force between

any two massesany two masses

This force is very small This force is very small compared to all the restcompared to all the rest

Newton came of with the Law Newton came of with the Law of Universal Gravitation, which of Universal Gravitation, which explains how we can find the explains how we can find the gravitational force of any objectgravitational force of any object

A large mass is required for A large mass is required for gravity to be feltgravity to be felt

Gravity is relational to Gravity is relational to distance distance and and massmass The further apart two The further apart two

objects are the objects are the lessless the the gravitational forcegravitational force

The The smallersmaller the masses, the masses, the less gravitational the less gravitational force.force.

Gravity still has pull over Gravity still has pull over millions and millions of millions and millions of miles apartmiles apart

As distance doubles the As distance doubles the force gets quarteredforce gets quartered

The Earth Moon SystemThe Earth Moon System The moon stays in orbit The moon stays in orbit

because of Earth’s because of Earth’s gravitygravity

It works very similar to a It works very similar to a centripetal forcecentripetal force

It pulls in on an objectIt pulls in on an object So as the moon follows So as the moon follows

this circular path, it’s this circular path, it’s gravitational force has an gravitational force has an

affect of Earthaffect of Earth..

SatellitesSatellites

Satellites stay in orbit with centripetal force Satellites stay in orbit with centripetal force of gravityof gravity

If it were to slow down it would lose If it were to slow down it would lose altitudealtitude

Satellite motionSatellite motion requires energy for the requires energy for the satellite to move forward, while orbiting satellite to move forward, while orbiting due to the centripetal force of gravitydue to the centripetal force of gravity ..