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Newton’s Third Law – Tier 1
Part 1: The Physics Classroom
While driving down the road, a firefly strikes the windshield of a bus and makes
a quite obvious mess in front of the face of the driver. This is a clear case of
Newton's third law of motion. The firefly hit the bus and the bus hits the firefly. Which of the
two forces is greater: the force on the firefly or the force on the bus?
For years, space travel was believed to be impossible because there was nothing that rockets
could push off of in space in order to provide the propulsion necessary to accelerate. This
inability of a rocket to provide propulsion is because... (choose one)
a. ... space is void of air so the rockets have nothing to push off of.
b. ... gravity is absent in space.
c. ... space is void of air and so there is no air resistance in space.
d. ... nonsense! Rockets do accelerate in space and have been able to do so for a long
time.
Many people are familiar with the fact that a rifle recoils when fired. This recoil is the result of
action-reaction force pairs. A gunpowder explosion creates hot gases that expand outward allowing
the rifle to push forward on the bullet. Consistent with Newton's third law of motion, the bullet
pushes backwards upon the rifle. The acceleration of the recoiling rifle is... (choose one)
a. greater than the acceleration of the bullet.
b. smaller than the acceleration of the bullet.
c. the same size as the acceleration of the bullet.
In the top picture (below), Kent Budgett is pulling upon a rope that is attached to a wall. In the
bottom picture, Kent is pulling upon a rope that is attached to an elephant. In each case, the force
scale reads 500 Newton. Kent is pulling... (choose one)
a. with more force when the rope is attached to the wall.
b. with more force when the rope is attached to the elephant.
c. the same force in each case.
Part 2: The Coin Flick
Explain this phenomenon using Newton's Third Law of motion.
Draw a diagram of your observations when flicking one coin.
Draw what you observe when flicking 2 coins then 3 coins at the row of 5 coins. Summarize
your understanding of the 3rd law of motion.
Think of another evidence and/or application of the law in your everyday lives.
Part 3: The Best Film on Newton’s Laws. Ever!
Notes you want to take as you watch:
Part 4: What were they thinking?
How Newton's Third Law applies to the situation viewed in the video? Be specific.
Part 5: Your Turn to Practice
Drawing and Labeling Action Reaction Force Pairs; In the example below the action force is described and
the arrow (vector) is drawn. The reaction force has been completed also. In the remaining pictures the
action force is described and drawn. You are to describe the reaction force and draw the reaction arrow
(arrows go tail to tail or head to head). Then draw your own action-reaction situation, describe the forces
and draw the arrows. Finally, figure out the forces at each of the contact points in the final drawing.
Action:
Force of fist on wall
Reaction:
Force of wall on fist
Action:
Force of ______ on _______
Reaction:
Force of______ on_______
Action: Force of ______ on ______
Reaction: Force of ______ on ______
Action:
Force of _____ on _____
Reaction:
Force of _____on _____
Action:
Force of _______ on ________
Reaction:
Force of _____ on ______
Action:
Force of ____ on ____
Reaction:
Action:
Force of ______ on _____
Force of ______ on _____
Reaction:
Force of ___ on ____
Draw and write your own here. Draw the picture, the arrows for both action and reaction and the
descriptions for the action and reaction forces
At each contact point draw the action and reaction forces and identify the amount of force at
each
The scale reads 60 N