Section 1: The Nature of Force

Force – a push or pull on an object; causes an object to accelerate.

0 m/s3 m/s

Calculating ForceForce = (mass)(acceleration)

F = mameasured in units of:

kilogram-meter/second squared(kgm/s2)

kilogram-meter/second squared

a.k.a.

Newton(N)

Two Types of Forcesbalanced forces – forces of equal

strength & acting in opposite directions; net force always equals

zero Newtons.

5 N5 N

Net force = 0 N

unbalanced forces – forces of unequal strength &/or act in different

directions; causes an object to move.

5 N 2 N

3 N

Net force =

3 N

Unbalanced Forces

5 N

3 N8 N

5 N

5 N

~7 N

Section 2: Friction & Gravity

friction- the force that two surfaces exert on each other when they rub against each other.

4 Types of Friction: (strongest to weakest)

1) Static2) Sliding3) Rolling4) Fluid

- air resistance is the most common form.

gravity – a force that pulls objects toward each other.

Gravity causes objects to accelerate toward earth at:

9.8 m/s2.

Gravity also causes:

Law of Universal Gravitation

states that due to gravity every object in the universe is attracted to every other object in the universe.

Weight

weight is the gravitational pull on an object.

weight = (mass)(gravity)

w = mg

measured in units of:Kgm/s2 a.k.a. Newtons

Calculate your REAL weight

Step 1) Find your mass:# of lbs / 2.2 = # of kgs.

Step 2) Calculate your weight

w = (# of kgs.)(9.8 m/s2)

Gravity in the Solar System

Moon 1.2 m/s2Venu

s7.98 m/s2

Jupiter 31,000 m/s2Su

n3,244,816.

1 m/s2

Newton’s First Law(Law of Inertia)

An object at rest will remain at rest, and an object in motion will remain in motion at a constant velocity, unless an unbalanced force acts upon it.

inertia – the tendency of an object to resist changes in its motion.

Newton’s Second Law

force, mass and acceleration are related with the formula:

F = ma

50 N

300 kg

6 m/s2

300 kg

100 N

12 m/s2

600 kg

100 N

6 m/s2

Newton’s Third Lawif one object exerts a force on another

object, then the second object will exert a force of equal strength in the opposite direction back on the first object.

FuelGas

momentum – the product of an object’s mass and velocity.

momentum = (mass)(velocity)

p = mv

measured in units of:kilogram-meter/second

Law of Conservation of Momentum

states that: the total momentum of a group of objects remains constant

in other words:

the total momentum of objects before a collision equals the total momentum after a collision.

8

1.5 m/s

0.25 kg

0 m/s

0.3 kg

C

Before the collision

p = (0.25 kg)(1.5 m/s)

p = (0.3 kg)(0 m/s)

p = .38 kgm/s

p = 0 kgm/s

pt = .38 kgm/s + 0 kgm/s

pt = 0.38 kgm/s

After the collision

8

0.25 kg 0.3 kg

C

0.75 m/s

p = (0.25 kg)(0.75 m/s)

p = (0.3 kg)(0.63 m/s)

p = 0.19 kgm/s

p = 0.19 kgm/s

pt = 0.19 kgm/s + 0.19 kgm/s

pt = 0.38 kgm/s

0.63 m/s