Problem

Does an apple exert a gravitational force on the Earth? If so, how large a force? Consider an apple (a) attached to a tree and (b) falling.

Step by step solution

Step 1</p>

Gravity may be defined as a force between objects with mass. Gravitational force is always attractive. , where G is gravitational constant, M mass of the Earth, m mass of the apple, r distance between the objects.

Step 2</p>

According to Newton’s second law, the gravitational force is giving to the objects on Earth acceleration g, acting on its mass.

Step 3</p>

According to Newton’s third law, for every reaction, there is an equal and opposite reaction. That is, if an object exerts force on another object, then the second object will exert the same amount of force on the first object but in the opposite direction So, basing on Newton's third law, apple also exerts force on earth that is equal in magnitude and opposite in direction to the force exerted by earth on the apple.