FORCE = Any push or pull which causes something to move or change its speed or direction

What is a Force?

Forces can be BALANCED or UNBALANCED

Balanced forces are equal in size and opposite in direction

UnBalanced forces are not equal in size and/or opposite in direction. If the forces on an object are UNBALANCED, we say a NET force results.

What is a Force?

Can you think of examples of forces?

Balanced Forces?

Unbalanced Forces?

What is a Force?

Force

I. ForceA. a push or pull that one body exerts on

anotherB. What forces are being

exerted on the football?

Fkick

Fgrav

Measuring Forces

I. Forces are measured in newtons (kg . m/s2).

I. Forces are measured using a spring scale.

Force

I. Balanced Forces

A. forces acting on an object that are opposite in direction and equal in size

B. no change in velocity

Force

I. Net Force

A. unbalanced forces that are not opposite and equal

B. velocity changes (object accelerates)

Ffriction

W

Fpull

Fnet

NN

ConcepTest 2You are a passenger in a car and not wearing your seat belt.

Without increasing or decreasing its speed, the car makes a sharp left turn, and you find yourself colliding with the right-hand door.

Which is the correct analysis of the situation? ...

ConcepTest 2

1. Before and after the collision, there is a rightward force pushing you into the door.

2. Starting at the time of collision, the door exerts a leftward force on you.

3. both of the above

4. neither of the above

2. Starting at the time of collision, the

door exerts a leftward force on you.

ConcepTest 1

TRUE or FALSE?

The object shown in the diagram must be at rest since there is no net force acting on it.FALSE! A net force does not cause motion. A net force causes a change in motion, or acceleration.

Taken from “The Physics Classroom” © Tom Henderson, 1996-2001.

GRAVITYGRAVITY: An attraction force between all masses

Newton’s universal law of Newton’s universal law of gravitationgravitation: Every object in the universe exerts a gravitational attraction to all other objects in the universe

The amount of gravitational force depends upon the mass of the objects and the distance between the objects

What is Gravity?

The greater the mass, the greater the forceforce

The greater the distancedistance, the lessless the force

Acceleration due to gravity = 9.8 m/s/s or 9.8 m/s2

What is Gravity?

Gravity

A.force of attraction between any two objects in the universe

B.increases as...

1.mass increases2.distance decreases

Gravity

I. Who experiences more gravity - the astronaut or the politician?

less distance

more mass

I. Which exerts more gravity - the Earth or the moon?

Gravity

I. Would you weigh more on Earth or Jupiter?

greater gravity

greater weight

greater mass

A. Jupiter because...

What is Motion?

Motion: A change in position of an object compared to a reference point

What is Friction?Friction = A force that opposes or

slows down motion Caused by the physical contact

between moving surfaces The amount of friction depends

upon the kinds of surfaces and the force pressing the surfaces together

Changes motion into heat

FrictionA. force that opposes motion

between 2 surfacesB. depends on the:

1. types of surfaces2. force between the

surfaces

FrictionI. Four Types of Friction

Static Friction – force that acts on objects that are not moving. (Couch Potato)

Sliding Friction - force that opposes the direction of motion of an object as it slides over a surface. (Ice skating or bobsledding)

Rolling Friction – friction force that acts on rolling objects. (Rollerblading)

Fluid Friction – force that opposes the motion of an object through a fluid. (Planes flying or submarines traveling)