FORCES
Unit F Chapter 1
CH 1 LESSON 1 INVESTIGATION

Directions
1.
Make a chart with
three columns
labeled: Object,
Prediction, Result.
2.
From your group of
objects predict what
objects will be
attracted by the
magnet.
INVESTIGATION CONT…
3)
Test each object and
record whether or
not the object is
attracted to the
magnet or not.
4.
Bar magnets have a
North and South
poles. Bring the
north-seeking pole
toward a southseeking pole…what
happens?
5.
Now bring two south
seek poles together
and two northseeking poles…what
happens?
CH 1 LESSON 1 EVERYDAY FORCES

What is a force?
Any push or pull that causes an object to move, stop,
or change speed and direction.
 An object ONLY moves, stops, or changes speed or
direction when a force acts on it.


What are 3 everyday forces?
1.
2.
3.
Friction
Magnetism
Gravitation
FRICTION
Friction is a force that
opposes, or acts
against, motion when
two surfaces rub
together.
 When you go sleigh
riding you keep
moving on the snow
because there is little
friction between the
snow and the sled.

MAGNETISM
Magnetism is the
force of attraction
between magnets and
magnetic objects.
 Every magnet has a
north and southseeking pole.
 Like poles repel.
 Unlike poles attract.
 Earth is surrounded
by a magnetic field.

GRAVITATION
Gravitation is the
force that pulls all
objects in the universe
toward another.
 The strength of
gravitation between
two object depends on
the distance between
them.
 Earth’s gravity keeps
the moon in orbit.

Remember: Force of
gravity pulls on both
objects.
 For example: If you
throw a ball in the air,
Gravity pulls the ball
toward Earth. Gravity
also pulls Earth
toward the ball.
Earth has more mass
than the ball so the
smaller object does
most of the moving

REVIEW QUESTIONS
1.
2.
3.
4.
5.
What starts an object moving or stops it if it is
already moving?
Name three everyday forces.
What force keep the moon in orbit around
Earth?
Suppose you push a cart toward the west. In
what direction does the force of friction push on
the cart’s wheels?
The force of gravitation is less when –
a.
b.
c.
d.
The total of the masses is greater
Friction between them is greater
The force of magnetism is greater
The distance between them is greater
CH 1 LESSON 2 FORCES THAT ACT
TOGETHER

Balanced Forces
Are equal in size and
opposite in direction.
 They cancel each other
out.
 When forces are
balanced an object’s
motion or direction
will not change.
 Because forces are
balanced it seems as if
no force is acting on
the object at all.


Unbalanced Forces
Occur when one force
is greater than its
opposite force.
 When unbalanced
force’s act on an
object, the object can;
start to move, speedup, slow down, stop or
change direction.
.

EXAMPLE OF UNBALANCED FORCES

When a football
player is tackled,
forces are
unbalanced. When
one player applies
more force than
another, the
opposing player is
stopped.
ACTING IN PAIRS
Forces ALWAYS act
in pairs.
 When you walk your
feet are pushing
against the floor, but
the floor is also
pushing against your
feet.

NET FORCE




We already know when
two forces act on an
object they will be
balanced or unbalanced.
The net force is adding
or subtracting
individual forces to find
the value of the
combined forces.
If forces are opposite
you subtract the smaller
force.
If forces are in the same
direction you add the
forces

1.
Example:
You TRY to push Ms.
Davis over with a force
of 130N. Ms. Davis is
soooo strong she
pushes back with the
force of 300N. What is
the net force?
300N – 130N = 170N
REVIEW QUESTIONS
1.
2.
3.
4.
5.
What happens to an object when balanced forces
act on it?
A moving object speeds up. Are the forces
acting on the object balanced? EXPLAIN.
Suppose you ride a bike along a flat, straight
road at a constant speed. Are the forces acting
on the bike balanced or unbalanced?
Two bumper cars collide. Both cars stop. How
do you know that a force has acted on both cars?
Suppose a book weighs 35 newtons and you
apply a force of 50 newtons to lift it. The net
force acting on the book is? Which direction?
ANSWERS
1.
2.
3.
4.
5.
It seems as if no force is acting on the object.
No, because the object’s speed increase so and
unbalanced force is acting on it.
Balanced, there is no change in motion or
direction.
The bumpers cars both stopped, therefore a
force had to act on it.
15 netwons, Up
CH 1 LESSON 3 INVESTIGATION
Create this chart below in
EXCEL:
Column A
Column B
Column C
Column D
Weight
Trial
(Newtons)
Height (meters) Work (Joules)
Example:
30N
1
2
3
4
2M
30N x 2m = 60J
DIRECTIONS
1.
2.
3.
4.
5.
Weigh the notebook on the table using the spring
scale and record its weight in Newtons under Trail 1
on the table.
Measure the total height of the stairs in meters and
record the measurement under Height in Trail 2. .
Work can than be calculated by multiplying the
weight x height = work. This can be done by using
the “Math Function” in Excel. (Demonstrate)
Suppose in Trail 2, you now carry your object 2
flights of stairs. Calculate your new height, and
amount of work done.
Continue this process up to Trail 4, continuing to
increase the flights of stairs.
DRAW CONCLUSIONS
1.
Compare the amount of work a person carrying
one notebook, one flight of stairs does, to a
person who has to walk three flights of stairs.
2.
Based on your data, interpret and draw
conclusions about how much work is related to
force and distance.
QUESTION OF THE DAY:
YOU STUDY FOR YOUR NEXT SCIENCE
TEST FOR 3 LONG HOURS. HOW MUCH
WORK HAVE YOU DONE?!
ANSWER: NONE!!!
So why have you not
done any work?
 The scientific
definition of work – is
the use of a force to
move an object
through a distance.
 So unless you were
walking and studying
at the same time, you
haven’t done work.


How we calculate
work.
Weight x Distance = Work

1.
Example:
If you move a 2000N
piano, 8m, how much
work have you done.
2000N x 8m = 16,000J
POWER
Power – is the amount
of work done for each
unit of time.
 AKA: how quickly you
complete work.
 The metric unit of
power is the watt.
 Formula for power:

Work ÷ time = Power
SIMPLE MACHINES

A machine is
something that makes
a task easier by
changing the size or
direction of the force,
or distance over which
the force acts.

6 types of simple
machines.
1.
2.
3.
4.
5.
6.
Pulley
Wheel & Axle
Wedge
Inclined plane
Screw
Lever
EVERYDAY MACHINES
Compound machine is
made up of two or
more simple
machines.
 A pencil sharpener is
a good example. It
combines wheel and
axel to turn the
sharpener, and a set
of wedges to sharpen.

NOT SO SIMPLE MACHINES

http://player.discoveryeducation.com/index.cfm?g
uidAssetId=604C7FB7-422E-4340-8215C5E7D77BDABB&blnFromSearch=1&productco
de=DSC
REVIEW QUESTIONS
1.
2.
3.
4.
5.
How much work is done if you life a 20-newton
weight 10 meters?
Which involves speed-work or power?
Look at the table of Pg. F18. How much power
is needed to life 1 piano 1 floor in 10 seconds?
Explain how a set of pulleys could help the
gardener mentioned on page F18 remove the
tree stump.
The amount of power needed to do 10joules of
work in 1 second is?
a.) 1 watt
b.) 10 joules
c.) 10 watts
d.) 1,000 watts
WEB ACTIVITY: SIMPLE MACHINES


http://www.edheads.org/activities/simplemachines/
Identify the different simple machines and their
functions in a variety of locations with this
interactive website.