Intro to Forces and Motion Ms. Graettinger Physical Science

What is a force?  Force is a push or pull on an object or by an object (interaction)  Balanced (no acceleration) or unbalanced (acceleration)  A force is that which changes or tends to change the state of rest or motion of a body.

Examples  Magnetic (push or pull)  Elastic (push or pull)  Compression (push)  Gravity (pull)  Tension (pull)  Friction (pull)

Newton’s 3 Laws  1 st : An object in motion stays in motion. An object at rest stays at rest-- until an outside force acts upon it  2 nd : F=ma  3 rd : For every action, there is an equal and opposite reaction

The Force Equation  F = ma  Force = mass x acceleration  Mass is in kg  Acceleration is in m/s 2  Force is in Newtons (N)

Force Equation Example  How much force is needed to accelerate a 70-kg rider and her 200- kg motorcycle at 4 m/s 2 ?  F=ma  F=(70kg + 200kg) x (4 m/s 2 )  F=1080 N

Falling Objects  Any two objects falling from the same distance, released at the same time, will land at the same time  Why is this?

Air Resistance  The force air exerts on a moving object  If there is no force except for gravity, all objects will accelerate at a rate of 9.8 m/s 2

Air Resistance  This force acts in the opposite direction to that of the objects motion  Air resistance pushes up while gravity pulls down

Air Resistance Example

Acceleration due to Gravity on Earth  Falling objects accelerate at 9.8m/s 2  Therefore,  Weight(N)=m(kg) x a  W=m x 9.8m/s 2