May the Force Be With You!

What is FORCE?• A push or pull on an

object• Causing resting

objects to move• Causing moving

objects to accelerate

Two Main Force Types

• Balanced Forces– Two Forces– Opposite directions– Both are equal in value– No movement

(stationary)

• Unbalanced Forces– Two Forces– One greater than the

other– Opposite directions– Movement

Newton’s 3 Laws of Motion

1st Law of Motion

• The Law– Objects at rest

remain at rest or objects in motion remain in motion unless acted on by a force

• AKA– Law of INERTIA

1st Law of Motion

• Inertia—force that is resistant to the direction of motion

• Concept—unbalanced forces

• Ex: – inertia belts (seat belts)– Space ships going

through space

2nd Law of Motion

• The Law– The acceleration of a

body depends on the ratio of the acting force to the mass of the body

• Concept– Unbalanced forces

• AKA– The force formula

Force Formula

• Force = mass * accelerationF= m*a

• F= force (unit = Newton)• m= mass (unit = kg)

• a= acceleration (unit m/s2

Force Example Problems

#1How much force is needed to accelerate a 500-kg car

at a rate of 4 m/s/s?

#2A 50-kg object is

accelerating at a rate of 2 m/s/s, what is the force

that caused this acceleration?

3rd Law of Motion

• The Law– For every action there is

an equal but opposite reaction

• Concept– Balanced Forces

• Ex– Stationary Objects– Rockets being launched

Applying the 3rd Law• If Rico kicked a

ball with 100-N of force, how much force did the ball exert on Rico?

What is Friction?

• Is a force that resist motion and can cause heat

• Allows us to walk, drive a car, play sports

• Lubricants help reduce friction

4 Types of Friction

• Static Friction– Friction force on

stationary objects– Ex: book sitting on desk

• Sliding Friction– Friction acting on

objects sliding over a surface

– Ex: pushing a box

• Rolling Friction– Friction acting on

objects that are rolling– Ex: car tired

• Fluid Friction– Friction acting on

objects going through a fluid

– Fluid—liquid or gas– Ex: swimming or air

resistance

ID the type of Friction

What is Gravity?

• A force that acts between masses• Acts downward• Acceleration due to gravity (on Earth)= 9.8 m/s/s

What is Air Resistance?

• Force that slows down falling objects

• Factors–Atmosphere– Surface area of

object

• Acts upward

Gravity and Air Resistance: A Relationship

• They are opposite forces

• Gravity goes down• Air resistance acts

up• Follows Newton’s 3rd

Law of Motion

Feather vs. Rock• EARTH– Feather floats down–Rock falls at 9.8

m/s/s–Why? • Air Resistance

• Moon or Vacuum– Feather and rock fall

at the same rate–WHY?• No air so no air

resistance

Projectile Motion

• The motion of falling objects throw forward

• Two forces– Gravity– Forward velocity

• Gravity acts down• Velocity acts forward• Forms a curve path

WeightIs the force of gravity acting on an object

Weight Formula•Weight = mass * gravity

•Fg = m * g•Fg= weight (unit = N)

•m= mass (unit = kg)•g= gravity (9.8 m/s/s)

Weight Example Problems

#1If a 20 kg dude is on

Earth, what is his weight?

#2A rock on Earth has a

weight of 1000 N, what is the rock’s

mass?