3rd Law of Motion
Action & Reaction
Do Now — Review
Describe the motion of these trucks
moving to the right.
Visualizing Newton's 3rd Law
Frank Noschese — John Jay H.S.
Action/Reaction — NASA
(right click, save as)
Which Way Is It Moving?
“Which way is the skater below moving?”
“All the forces in the universe, would be:
a) an even number b) odd c) unknowable”
3rd Law of Motion
“Press on a rock and the rock presses on you
(with an equal, but opposite force)”
— Newton
[ Flash ]
Skateboarder [ HTML5 ]
Skateboarder 2 [ HTML5 ]
Lamp & Table
A lamp applies a force of 10 N to a table.
What force does the table
apply on the lamp?
Which direction is this force applied?
[ Flash ]
Earth & You
Earth pulls down on you.
That's half the story…
Explain this phenomena using one or more
of Newton's Laws of Motion
Magnetically Coupled Pendula 2
School Blocks YouTube?
Use the file below.
Magnetically Coupled Pendula 2.mov
The more active bouncing magnet applies a force on the slower magnet on the opposite side. By applying a force it receives a force and therefore slows down.
3rd Law of Boxing Gloves
Physics of a Boxing Glove Discussion
Paul Hewitt Question
A heavy rock and a light rock in free fall (zero air resistance) have the same acceleration. The reason the heavy rock doesn't have a greater acceleration is that the
A. force due to gravity is the same on each.
B. air resistance is always zero in free fall.
C. inertia of both rocks is the same.
D. ratio of force to mass is the same.
E. None of these.
Isaac Newton
NYSSLS Reading Passage · Dynamics
The Bug and the Windshield: What Newton's Third Law Really Says
Open Reading Passage → Regents Practice Version →
Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. Which statement is Newton's 3rd Law?
2. A lamp pushes down on a table with a force of 10 N. What force does the table exert on the lamp?
3. Earth pulls down on a student with a force of 600 N. What force does the student exert on Earth?
4. A bug hits the windshield of a fast-moving car. Which force is bigger?
5. With no air resistance, a heavy rock and a light rock fall with the same acceleration. This is because…
Ice Skaters Push Apart
Two ice skaters stand at rest facing each other on smooth ice. Skater A has a mass of 50. kg and skater B has a mass of 75 kg. They push on each other’s hands and move apart.
Which statement correctly compares the forces the skaters exert on each other?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. If each skater pushes with a force of 150 N, what is skater A’s acceleration?
C2. Skater A stands on the left and skater B on the right. During the push, skater B accelerates at 1.6 m/s². Choose the direction of the force skater A exerts on skater B, and determine its magnitude.
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C3. During the push, each skater exerts a 120-N force on the other. Substitute numerical values into a mathematical representation that can be used to determine the magnitude of skater A’s acceleration. Then calculate the acceleration.
C4. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship.
C5. Why don’t the equal and opposite forces between the skaters cancel out, leaving them motionless?
C6. An astronaut drifts a few meters away from the International Space Station with no tether, holding only a heavy wrench. Describe how she could use Newton’s third law to get back to the station. Identify the action–reaction force pair.
