"Every action has an equal and opposite reaction."

Newton’s Third Law is probably understood best by looking at an example of it in action. If you lean against a wall with your hands and push on the wall softly, your body pushes away from the wall softly. If you push on the wall hard, your body pushes away from the wall harder. This is what Newton meant when he said the reaction is equal.

So what was Newton talking about when he said there was an opposite reaction? Again, let’s look at an example. If you’re floating in the water and you push against the pool wall, your push makes you go in the opposite direction, away from the wall. Another example is if you’re floating on a raft and you want to go the direction your head is pointing. You put your hands in the water and push your hands toward your feet. This makes you and the raft go in the direction your head is pointing. Your hands pushing against the water in one direction is an action and you and the raft moving in the other direction is an opposite reaction.

Take a Newtonian Demonstrator and drop one of the balls on the end. When it hits the next ball, the first ball applies force to the second ball. The second ball hits the third ball, and the force is transferred. The third ball does the same to the fourth ball, which does the same to the last ball. The last ball then swings out and away from the other balls.

So how does this all happen? The first ball applies a force to the second ball, so the second ball moves to the left. Newton’s Third Law says that the second ball also applies an equal and opposite force to the first ball. So guess what happens to the first ball? It comes to a stop!

Then guess what happens? Newton’s First Law tells us the last ball will stay in motion until an outside force acts upon it. The last ball finally gets pulled back toward the fourth ball by gravity, and the whole thing starts over again in reverse.

If you drop the balls on both ends at the same time, they both apply the same force to the inside balls. When the two equal forces meet each other, they don’t have anywhere else to go. Since the forces are equal, they neutralize (stop) each other.

Newton’s Third Law also explains how rockets are launched. The force of the burning fuel coming out of the bottom of the rocket creates an action. The equal and opposite reaction is the rocket being pushed (launched) in the opposite direction.

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