Intro to Forces and Motion

Ms. GraettingerPhysical Science

What is a force?

Force is a push or pull on an object or by an object

Force= mass x accelerationF=maA force is that which changes

or tends to change the state of rest or motion of a body.

Newton’s 3 Laws

1st : An object in motion stays in motion. An object at rest stays at rest--until an outside force acts upon it

2nd : F=ma3rd : For every action, there is an equal and opposite reaction

The Force Equation

F = ma

Force = mass x acceleration

Mass is in kgAcceleration is in m/s2

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/s2?

F=maF=(70kg + 200kg) x (4 m/s2)

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?

Acceleration due to Gravity

Falling objects accelerate at 9.8m/s2

Therefore,Weight=m x aW=m x 9.8m/s2

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/s2

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

Classwork:Everyone must calculate how much they really weigh in Newtons.

Conversion factor: 1kg=2.2 lb