Rowan drives a nail with a hammer. The nail sinks into the wood.
But watch the hammer: it stops dead on contact. Something exerted a force on the hammer too. What?
The nail did. Forces never come alone. Newton noticed that they always come in pairs, and his third law says exactly how the two compare.
Start with the hammer and the nail: the hammer pushes down on the nail while the nail pushes up on the hammer.
That second force is real. It is what stops the hammer dead.
The same pairing shows up everywhere. A sprinter's shoe exerts a backward force on the track, and the track exerts a forward force on the shoe.
Two bumper cars collide. Each car exerts a force on the other, at the same instant.
Newton's third law names the pattern: when object A exerts a force on object B, object B simultaneously exerts a force on object A.
The two forces are equal in magnitude and opposite in direction.
Tilda says: 'While a tennis racket's strings exert a force on the ball, the ball exerts a force of the same magnitude back on the strings.' Is she correct?
They are also the same type of force. A contact force pairs with a contact force. A gravitational force pairs with a gravitational force.
The two act at the same instant. Neither comes first, and neither causes the other. They are two sides of one interaction, and together they are called an interaction pair, or a third-law pair.
When a bat strikes a baseball, the bat exerts a force on the ball. Which statement completes Newton's third law for this case?
The law never skips a case. When a loaded barge bumps a small tugboat, the force on each from the other has the same magnitude, whatever the two masses are.
A loaded moving truck and a small car collide head-on. During the collision, how does the force on the car from the truck compare with the force on the truck from the car?
A canoe paddle exerts a 40 N backward force on the water. State the force the water exerts on the paddle.
Newton's third law: the water exerts a force back on the paddle, at the same instant.
Equal magnitude: 40 N.
Opposite direction: forward.
Same type: a contact force.
The water exerts a 40 N forward contact force on the paddle.
The Earth exerts a 700 N downward gravitational force on a skydiver. How large is the gravitational force the skydiver exerts on the Earth, and which way does it point?
The two forces of an interaction pair are equal in magnitude and opposite in direction.
So the skydiver exerts a gravitational force on the Earth of the same 700 N magnitude.
It points upward, toward the skydiver's position: opposite to the force on the skydiver.
700 N, upward, acting on the Earth.
A magnet holds a steel paper clip in the air. The magnet exerts a 2 N magnetic force on the clip. Which statement gives the force the clip exerts on the magnet?
Imre's skateboard rolls toward a wall. He reaches out, and his hand exerts a 90 N force on the wall. The wall does not move. Which statement about the force on Imre's hand is correct?
Which statement about the two forces of a Newton's-third-law pair is correct?