Net Force, Newton's Laws, & Free Body Diagrams

Ex of 3rd law A. full grocery cart requires more force to push than an empty cart B. pushing backward in order to move forward while ice skating C. cookie sitting on plate D. none of above

B. pushing backward in order to move forward while ice skating

Which is ex of 1st law A. Using force to push a box B. Pulling back arrow to shoot it forward C. table remains motionless in a classroom D. None of the above

C. table remains motionless in a classroom

Newton's 3rd Law

For every action there is an equal and opposite reaction

Newton's 2nd Law

the acceleration of an object depends on the force exerted on it and its force

A bird pushes down on the air with its wings in order to fly.

3

The air is let out of a balloon and it flies around the room.

3

A fireman turns on his hose & is knocked backwadards

3rd

Balanced Force

= forces that act on the object speed and direction doesn't change(NF always 0)

A baseball continues to roll until friction, gravity, and air resistance stop it.

1

A person's body is thrown outward as a car rounds a curve on a highway.

1

A soccer ball will not move until a player kicks it

1

Free Body Diagram

1. Sketch what is happening 2. Determine forces that act upon object -Normal Forces(N, up) -Friction(Ff, left) -Gravity(Fg, down) -Force Applied/Tension(Fa/Ft, Right) 3. Draw object & the forces acting on it

It requires more force to pull a wagon w/ someone in it than an empty wagon

2

Pushing a child on a swing is easier than pushing an adult on the same swing.

2

How do you calculate Net Force

1. add all forces in same direction 2. subtract forces in the opposite direction(bigger # - by smaller #) 3. determine which direction force is acting(the arrow/object that has greater NF) 4. balanced or unbalanced (will only be balanced if NF is 0) How you should write NF: amount of NF direction bal/unbal

A motorcycle will accelerate faster than a large truck.

2nd

Net Force

combination of all forces acting on an object determines which direction it moves

Which best represents inertia

object at rest remains at rest object in motion remains in motion flying forward when a car suddenly stops

Newton's 1st Law

object will stay at rest and object in motion will stay in motion at the same speed and direction unless acted on by an unbalanced force

Unbalanced Forces

un= forces that act on object results in a NF speed and direction of an object changes