WARM UP

• Fill out the chart to show your understanding of

MASS, WEIGHT, and GRAVITY

MASS WEIGHT GRAVITY

THE CAUSE OF FORCES

• A force is an action that has the ability to

change motion. It is a push or pull

• Forces can increase or decrease the speed of a

moving object.

• Forces can also change the direction in which

an object is moving.

FOUR ELEMENTAL FORCES

All forces in the

universe come

from only four

basic forces.

UNIT OF FORCE

• The newton (N) is a metric unit of

force.

• 1 pound (lb) equals 4.448 N.

• If one pound of force equals 4.448

newtons, then a 100 lb person weighs

444.8 newtons

STRONG NUCLEAR FORCE

• This force holds the nucleus

of an atom together.

• This is a very strong force

but only reaches a short

distance.

ELECTROMAGNETIC FORCE• The electromagnetic force acts between

charged particles – protons and neutrons -

and is the combination of all electrical and

magnetic forces.

• This force holds atoms together in

molecules.

WEAK FORCE• The weak force is stronger than gravity, but

it is only effective at very short distances.

• Causes Radioactive Decay

• Only occurs at a subatomic level

GRAVITY

• The force of gravity on an object is called weight.

• At Earth’s surface, gravity exerts a force of 9.8 N on every kilogram of mass.

WEIGHT VS. MASS

• Weight and mass are

not the same.

• Mass is measured in

kilograms (kg).

• Weight is a force

measured in newtons

(N).

• Weight depends on

mass and gravity.

CALCULATING WEIGHT

Direct Relationship

SOLVING PROBLEMS

• Calculate the weight of a 60-kilogram person (in newtons) on Earth and on Mars.

1. Looking for: – …weight of person in newtons on both

planets– Given: – …mass = 60 kg; g = 3.7 N/kg on Mars; – …implied g = 9.8 N/kg on Earth

2. Relationships: – W = m x g

3. Solution: – 60 kg x 9.8 N/kg = – 60 kg x 3.7 N/kg =

CONTACT FORCES

• Contact force. ... Pushing a car up a hill or kicking

a ball or pushing a desk across a room are some of

the everyday examples where contact forces are

at work.

• Examples of contact forces are applied,

gravitational, normal and frictional

APPLIED FORCE

• An applied

force is

a force that

is applied to an

object by a person

or another object.

A person is pushing a desk

across the room, is

applying a force upon

the object. The applied

force is the force exerted

on the desk by the person.

GRAVITATIONAL

The force of

attraction between all

masses in the

universe; especially

the attraction of the

earth's mass for

bodies near its

surface.

NORMAL FORCE

The normal

force is the

support force exert

ed upon an object

that is in contact

with another stable

object.

For example, if a book

is resting upon a

surface, then the

surface is exerting an

upward force upon

the book in order to

support the weight of

the book.

FRICTIONAL FORCE

Frictional

Force refers to

the force

generated by two

surfaces that

contact and slide

against each other.

WE DO

Force Review Activities

(~ 20 min each activity)

• 4 Fundamental Forces Chart

• Mass/Weight/Gravity Practice

• Phy Sci Textbook Review Qs