Forces

What is a force?A force is a push or pull from one

object to another object

Examples: Earth’s gravitational pull on us, you pushing a chair, a table supporting a book

What is a force?

All forces have both size and

direction

The unit of force is the Newton

(N)

What other concepts have both a

size and direction?

Net ForcesThe net force is the combination

all of the forces acting on the object

Whenever more than one force act on an object, always sum the forces into a single net force

Forces in the Same DirectionWhen forces act in the same

direction, you add the forces together

The net force will be in the same direction as the two original forces

F1= 5 N

F2= 3 N

Fnet= 8 N

Forces in the Opposite Direction

When two forces act in opposite directions, you subtract the smaller force from the larger force

The net force will be in the direction of the larger force

F2= 7 NF1= 2 N Fnet= 5 N

Balanced ForcesWhen the sum of the forces

acting on an object equals zero, the forces are said to be balanced.

Balanced forces are equal in size and opposite in direction

Balanced Forces- Newton’s 1st LawThere is no change in motion

when the forces are balanced.

A stationary object remains

stationary

A moving object has constant

velocity

Unbalanced ForcesWhen the sum of the forces are

non-zero, there are unbalanced forces acting on the object

Unbalanced forces produce a change in motion, so they are necessary to cause accelerated motion

The Big Idea

Unbalanced forces result in a net

forceThe net force causes the object

to accelerateThis acceleration can be

predicted and described

Force, Mass, and AccelerationAn object accelerates when a net

force acts upon it

The net force is equal to the mass times the acceleration:

F = maThis relationship is Newton’s 2nd

Law

Force, Mass, and AccelerationThe acceleration of the object

depends on both the forces acting on the object and the mass of the object

The net force and acceleration are always in the same direction!!

F2= 7 NF1= 2 N Fnet= 5 Na

Example 1How much force is needed to

accelerate a 30 kg scooter at a rate of 1 m/s2?

F = ma

F = (30 kg) x

(1m/s2)

F = 30 N

Example 2How much force is needed to

accelerate a 0.5 kg baseball at a rate of 0.04 m/s2?

F = ma

F = (0.5 kg) x (0.04

m/s2)

F = 0.2 N