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## Middle school physics - NGSS

### Course: Middle school physics - NGSS>Unit 1

Lesson 3: Action and reaction forces

# Action and reaction forces

NGSS.MS:
MS‑PS2‑1
,
MS‑PS2.A.1
,
MS‑PS2.A
Whenever two objects interact with each other, each object exerts a force of equal strength on the other. However, each of these forces, while equal in strength, are in opposite directions.  Created by Sal Khan.

## Want to join the conversation?

• OK, let's accept Sal's explanation. If, however, there's equal forces at play with both the jet plane and the rocket, how do those objects actually move? By the explanation, doesn't one force acting equally against the other prevent some kind of "forward" motion? Any insight is welcome. And thanks Sal!
• if you throw a ball on the floor with a force of 150 newton (newton is the si unit of force) a force of 150 newton is exerted on the molecules of the floor . each molecule then exerts the same force of 150 newton not on itself but the ball so it bounces upward (if the ball doesn't bounce upward it doesn't mean that the reaction force of the molecules balance out but because the reaction force is not enough to move the ball move , the amount of force need to move the ball depends on the mass of the ball) Hope this helps!
• I do not understand this "And it's actually not that the Moon is rotating around the Earth. It's actually, they're both rotating around the center of mass of their combination" could you explain more ?
• The Earth and the Moon are exerting force on each other, but due to Earth's much larger mass, it doesn't move as much. They're still orbiting that center, but the Moon moves much more because its mass is smaller. It appears that the Moon is orbiting the Earth because Earth "orbits" the Moon so little. Earth's mass is greater than the Moon's, so it also has more gravity that pulls the Moon to orbit that center more than the Earth itself.
• This is easy
• Why do the force act on different things (points) and not on the same things (points)?
• If a rock falls to the ground what will the ground do?
• The ground will do nothing.
(1 vote)
• Interesting example
• So, Newton's 3rd law,
opposite and equal reaction means that something, whatever it may be, is going in the opposite direction than of the force applied but with the same reaction as in equal force/acceleration. Right?
I just want to make sure I've got this straight in my head.