Gravity and Friction

FORCES

Friction, Gravity and

Magnetism

What is a Force? Review…

A push or a pull on an object in a

particular direction.-

*Described by direction and strength

CONTACT FORCES

Does not require contact:

NON-CONTACT FORCES (P.634)

Force through CONTACT:

*Virtually all actions require a…

Magnetic

:

Gravity:

Forces are measured in
NEWTONS

Friction:

Multiple Choice

Forces are described by their _______ &_______

• balanced and unbalanced

• mass and distance

• strength & direction

• roughness and force

GRAVITY

An attractive force that exists

between all objects that have mass.

This force is dependent on mass

and distance from the object.

WEIGHT VS MASS

What is the difference?

Weight: Is the gravitational force exerted

on an object.

Your weight is actually a force measured in Newtons.

Mass:
Amount of matter in an object.

Demonstration: Mass & Gravity

LINK

And this link

Multiple Choice

_______________ is the measure of the amount of gravity acting on an object

• Mass

• Weight

• Net Force

• Newtons

GRAVITY AND AIR RESISTANCE

Most objects falling through air

experience a type of fluid friction called
air resistance.

Air resistance is not the same for all

objects.

The greater the surface area of the object

the greater the air resistance. (paper drop)

However, since the elephant has more

mass, it has more downward force of
gravity and falls faster.

GRAVITY AND FREE FALL

An object is in free fall when the only

force acting on the object is gravity.

Free-falling objects do not encounter

air resistance.

In free fall, the force of gravity is an

unbalanced force.

Gravity Tube Demonstration

Take away ALL
air, so that only
the force of
Gravity is being
used.

TRY THIS

AS A REVIEW,
WHAT IS THE DEFINITION OF GRAVITY?
A force that a

Check what
you’ve learned!

AS A REVIEW,
WHAT IS THE DEFINITION OF GRAVITY?
A force that acts between any two
masses. It pulls objects together.

Earth’s
gravity
(force)
pulls cat
downwards
towards
center of
Earth.

Check what
you’ve learned!

FORCE OF GRAVITY -

All objects in free fall accelerate at the same rate –
9.8 m/s² - regardless of their mass.

Multiple Choice

Acceleration due to gravity on Earth, g, is ____ m/sec2.

• 4.9

• 19.6

•  9.8 

• 39.2 

Multiple Choice

___________________ is affected by the distance between the objects and the amount of mass.

• Friction

• Weight

• Force

• Gravity

Multiple Choice

As mass increases; gravity ________________.

• Increases

• Decreases

WHAT IS FRICTION?

Friction is a force that resists the

motion of two surfaces that are
touching.

object, friction is the opposing force that slows or
stops the moving object.

When a moving object comes in contact with another

WHAT IS FRICTION?

*Sliding...resists objects while they are moving

*Fluid…air or water
*Rolling …wheel, roller, or ball

*Static. Prevents objects sliding

Without friction, an object would continue to move

at constant speed forever.

The strength of the force of friction depends on

the type of surfaces and how hard the surfaces
push together.

Rough surfaces produce greater friction than

smooth surfaces.

TRY THIS

Or This

AS A REVIEW,
WHAT IS THE DEFINITION OF FRICTION?
A force that

Dog moves to the right

Friction
force (left)

Check what
you’ve learned!

AS A REVIEW,
WHAT IS THE DEFINITION OF FRICTION?
A force that opposes the motion of objects that
touch as they move past each other.

Dog moves to the right

Friction
force (left)

Check what
you’ve learned!

Multiple Choice

Which of the following shows the direction of the friction force?

• A

• B

• C

• D

MAGNETISM

Magnetism is

the force of
attraction or
repulsion
between
magnetic
poles.

A MAGNETIC FIELD EXISTS AROUND A
MAGNET OR ANY MOVING CHARGED
OBJECT.

Magnetic fields are like electric fields or gravitational

fields in that they allow magnets to interact without

touching.

Multiple Choice

A snowball rolling down a grassy hill

• Gliding friction

• Static Friction

• Rolling Friction

• Air Resistance

Multiple Choice

A parachute falling to the ground.

• Air Resistance

• Static Friction

• Magnetism

• Rolling Friction