newton’s third law of motion building science champions
Post on 18-Dec-2015
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In thoughthttp://www.wimp.com/spaceshuttle/
After watching the Discovery launch, explain how Newton’s three laws are used by NASA scientist to launch a space shuttle.
Objectives State Newton’s third law of motion
Define and calculate momentum and state the law of conservation of momentum
Newton’s Third Law of Motion
Newton realized forces are not one direction
One object exerts a force on the second; while the second exerts a force back on the first
Second’s force is equal to and opposite of the first
First force is action and the second force is reaction
IF ONE OBJECT EXERTS A FORCE ON ANOTHER OBJECT, THEN THE SECOND OBJECT EXERTS A FORCE OF EQUAL STRENGTH IN THE OPPOSITE DIRECTION ON THE FIRST OBJECT
IMPORTANT
Force PairsForces in Newton’s 3rd law depend on each other
Force pair – is the force two objects apply to each other
Why don’t equal but opposite forces cancel each other out? Because each force acts on a different object
The person is pushing on the diving board The diving board is
pushing on the person
2 separate forces
Equal but Opposite
Action ForceReaction
Force
Equal
Opposite
When contact between the two players is made the forces are equal.
The players flying backwards is the opposite force.
The ground is the unbalanced force that will stop the players fall.
The force the white player hits the blue player with is transferred to the blue player and that is equal to the force that he will fall with.
Action-Reaction in Action A squid brings water in, then expels it to move
Action expulsion of water
ReactionSquid moves forward A space
shuttle burns fuel to create thrust, a pushing force, the ground pushes back on the shuttle
Reactio
n
Action
Momentum Momentum (p) – is the product of an object’s
mass and it’s velocity
p = mv
Mass is measures in kilograms (kg) and velocity is measured in meters per second (m/s)
Momentum is also described by it’s direction as well as its quantity
Momentum Problem Which has more momentum: a 3-kg
sledgehammer swung at 1.5 m/s or an 4-kg sledgehammer swung at 0.9 m/s?
Momentum = mass x velocity
3 kg x 1.5 m/s = 4.5 kg x m/s
4 kg x 0.9 m/s = 3.6 kg x m/s
Practice Problems
Golf ball = 0.72 kg x m/s baseball = 0.98 kg x m/s
A golf ball travels at 16 m/s, while a baseball moves at 7 m/s. The mass of the golf ball is 0.045 kg and the mass of the baseball is 0.14 kg. Which has greater momentum?
What is the momentum of a bird with a mass of 0.018 kg flying at 15 m/s?
Bird = 0.27 kg x m/s
Conservation of Momentum
Law of conservation of momentum – the total momentum of the objects that interact does not change
Quantity of momentum is the same before and after they interact
Total momentum of any group of objects remains the same unless outside forces act on the objects
Conservation refers to conditions before and after an event
A quantity that is conserved is the same after an event as it was before the event
Types of CollisionsObjects collide with one another in two different ways
Elastic collision – when colliding objects bounce off one another in the collision
Inelastic collision – when colliding objects stick to another
No matter the type of collision, the total momentum will be the same before and after the collision
Two Moving Objects Look at the two trains traveling in the same direction, train 1 is traveling at 10 kmph and train 2 is traveling at 5 kmph
10 kmph
5 kmph
When the trains collide the speed of each car changes
Train 2 is now traveling at 10 kmph and train 1 is now traveling at 5 kmph
10 kmph 5
kmph
Momentum is conserved – the momentum of one train decreases while the momentum of the other increases
One Moving ObjectCue ball is moving toward the stationary billiard balls
Stationary
Moving
The momentum from the cue ball is transferred to all the other billiard balls
Cue ball will become stationary, the stationary billiard balls will go in motion
Stationary
Momentum
The momentum is the same before and after the collision. This time the momentum from the cue ball is transferred to numerous other billiard balls.
Two Connected ObjectsInstead of objects bouncing off of each (elastic collision) other sometimes they will remain connected (inelastic collision)
Player A is running at 4 m/s and player B is stationary
4 m/s
Stationary
Once contact is made, the two players will share the momentum of player A
2 m/s
2 m/s
The momentum of the two players is still conserved
ReviewMomentum’s formula is p=mv
Elastic collisions the objects bounce off one another
Inelastic collisions the objects stay connected
Reactions are opposite but equal to the action
Newton’s third law is action/reaction
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