Reaction (physics)

Likewise, the spinning wheels of a vehicle attempt to slide backward across the ground.

The Earth, among other planets, orbits the Sun because the Sun exerts a gravitational pull that acts as a centripetal force, holding the Earth to it, which would otherwise go shooting off into space.

Since the Sun's mass is so much larger than Earth's, the Sun does not generally appear to react to the pull of Earth, but in fact it does, as demonstrated in the animation (not to precise scale).

A correct way of describing the combined motion of both objects (ignoring all other celestial bodies for the moment) is to say that they both orbit around the center of mass, referred to in astronomy as the barycenter, of the combined system.

Because of these accelerations (and subsequent decelerations), we conclude from Newton's second law that a net force is responsible for the observed change in velocity.

That this nearness is caused by a decision of the player has no bearing on the physical analysis.

[4] One problem frequently observed by physics educators is that students tend to apply Newton's third law to pairs of 'equal and opposite' forces acting on the same object.

Since the book is not accelerating, these forces must be exactly balanced, according to Newton's second law.

They are therefore 'equal and opposite', yet they are acting on the same object, hence they are not action-reaction forces in the sense of Newton's third law.

A possible cause of this problem is that the third law is often stated in an abbreviated form: For every action there is an equal and opposite reaction,[8] without the details, namely that these forces act on two different objects.

This causal relationship is not due to the third law but to other physical relations in the system.