# Science

posted by .

I have a science question that I don't quite understand.

Would you have to to have physical contact to exert a force?

Not necessarily. Could we blow very hard and exert a force on something? When I was a kid I liked to make paper pin wheels and blow on them to see the pin wheels turn.

1st Law: A body in rest tends to stay at rest, and a body in motion tends to stay in motion, unless the body is compelled to change its state. The evidence supporting the first part of this statement is easily seen. We know that a wheel will not begin rolling by itself. However, we do not see the proof of the second half in our world. That is because there is an ever present inhibiting force known as friction that acts as the external force resisting perpetual motion.

2nd Law: The second law is a formula--- Fnet = ma or A=F/m. The product of the object's mass (m) times its acceleration (a), is equal to the net force (Fnet) . Acceleration and force are vectors; in this law the direction of the force vector is the same as the direction of the acceleration vector. The acceleration of a body is dependent upon both the mass of the object (not its weight) and the net force perpetuating the motion (total force in the direction of the motion minus the force resisting motion). In the formula, a resisting force would be written as negative to produce a negative acceleration, which means the object would be slowing down.

3rd Law: For every action there is an equal and opposite reaction. This means that if I push you, I will be slightly pushed back in the process. This is the principle at work behind how jet planes and rockets propel themselves. They expel gases in the opposite direction, are pushed themselves in the process, and therefore move forward.

Motion, or a change in motion, occurs when a force is applied to an object. Motion has two components, speed and direction. A change in motion may mean a change in an object's speed, direction, or both. An object is said to be in motion only if it is changing its position with respect to a point of reference whose position is fixed.

Hello I am doing a science project that involves design and building a doorbell. Could you please give me some ideas on how to build a door bell and some useful materials.