Force and Motion Review

Motion is a change in position.

Speed is the distance an object travels in a certain amount of time.

Velocity is the speed and direction of a moving object.

Inertia is an object's tendency to resist a change in motion.

A force is a push or a pull on an object.

Force can be calculated with a formula:

force = mass x acceleration

(F=m x a)

Force is measured in units called Newtons (N).

Unbalanced Forces-When two forces acting on an object are not equal in size, we say that they are unbalanced forces.  Motion changes when we have unbalanced forces

When an object is at rest on a surface, such as the ground, its weight is balanced by the reaction force from the ground. The ground pushes up against the object. There is no acceleration with balanced forces.

Did you know that gravity is a force? When the only force acting on an object is gravity, the object is in a state called "free fall"

Another force to note is air resistance. Air resistance is a force that opposes the motion of objects that move through the air.

Newton's 2nd law states that The greater the mass of an object, the more force it will take to accelerate the object. 

This also ties in to inertia, an object's tendency to resist a change in motion. The greater the mass an object has, the greater inertia it will have.

Friction is a force opposing the motion between two surfaces. For example: Tires on roadway.

Sliding Friction is friction that occurs when one solid surface slides over another.

Static Friction is friction that acts on objects that are not moving.

Fluid Friction is friction on a solid object as it moves through a liquid or a gas.

Rolling Friction is when a wheel, ball, or cylinder rolls freely over a surface, as in ball and roller bearings