The document discusses various types of energy and forces, explaining that energy cannot be created or destroyed, only changed in form, and defines work as the ability to cause change when a force acts over a distance. It also explains Newton's three laws of motion, including that an object at rest or in motion will remain as such unless acted on by an unbalanced force, and that for every action there is an equal and opposite reaction. The document provides examples and formulas to help understand these concepts of energy, forces, and motion.

1. Work
Motion
Energy
7th Grade Science
Ms. DeFreese
September 25, 2012

2. Energy
The ability to
do work and
cause
change.

3. Law of Conservation of Energy
Energy cannot be
created or destroyed
Energy may change
form, but the total
amount remains the
same

4. Kinds of Energy
Potential Kinetic
– Energy at rest – Energy of motion
(stored energy) (moving energy)

5. Force
A push or pull that could cause a
change in an object’s motion

6. Balanced or Unbalanced
Balanced forces = no change in motion
– Often referred to as equilibrium
Unbalanced forces = change in motion

7. Measuring Force
Force can be
measured using a
spring scale
Measured in newtons
(N)

8. Force and Work
Force can produce work if acted over a
distance.
Work can be calculated by
w=Fxd
Force can be calculated by
F=w÷d

9. Gravity
A force or attraction
that exist between any
two masses.
– Gravity depends on the
MASS of objects and
DISTANCE between them
– GREATER MASS or
SMALLER DISTANCE =
STRONGER GRAVITY

10. Mass
The amount of matter in something
– Measured in GRAMS or KILOGRAMS
– Never changes . . . Remains constant

11. Weight
FORCE that GRAVITY
exerts (has) on a mass
– Measured in newtons (N)
– Changes depending on
relationship between mass
and gravity

12. Measuring Weight
Example: You weigh 120 pounds on Earth
– Gravity on the moon is 1/6 of that on Earth
• Your WEIGHT on the moon = 1/6 of your weight on
Earth (on moon you would weigh 20 pounds)
• Your MASS on the moon = your
mass on the Earth
• What you are made of (mass) does
not change… it remains constant

13. Assignment
Complete “Understanding Forces
Concept Map”
When complete, glue this in your
science journal
We will grade this at the beginning of
class tomorrow.

14. What is work?
Work is done when a force causes an
object to move in the same
direction that the force is applied.
The object must move.

15. Units of Measure
Force is measured in Newtons (N)
Distance is measured in meters (m)
Work is measured in Joules (J)
1 J = 1 N/m

16. Is it work?
A Joule is the amount of work done, BUT if
work is to be done, then the object has to
be moved in the same direction as the
force.
If you spent ½ hour pushing on a parked car,
you were tired, hot and sweaty, you may feel
like you have worked, but if the car never
moved then you did NO work.

17. Example
A force of 10 Newtons, that moves an object 3
meters, does 30 n-m of work.
W = F x D (W = FD)
W = 10N x 3m
30 N/m = 10N x 3m
W = 30 Newton-meters
A Newton-meter is the same thing as a joule

18. Work or No Work?
Even though he is exerting force, nothing is being moved
a distance, therefore no work is being done.

19. Work or No Work?
Force is being exerted and an object (fire
truck) is being moved.

20. Motion
The process of moving from one
place to another
3 kinds:
–Straight (walking)
–Circular (Bicycle Wheel)
–Vibration (Guitar
String)

21. Sir Issac Newton & the Laws of Motion

22. Newton’s First Law of Motion
An object at rest will remain at rest
unless acted on by an unbalanced
force. An object in motion continues in
motion with the same speed and in the
same direction unless acted upon by
an unbalanced force
What does this mean?

23. What it means…
There is a natural tendency of
objects to keep on doing what they're
doing.
In the absence of an unbalanced
force, an object in motion will
maintain this state of motion.

24. Example 1
What is the motion in this picture?
What is the unbalanced force in
this picture?
What happened to the skater in
this picture?

25. Example 2
This law is the same reason why
you should always wear your seat
belt.

26. Newton’s Second Law of Motion
Acceleration is produced when a force
acts on a mass.
The greater the mass (of the object
being accelerated) the greater the
amount of force needed (to accelerate
the object).
What does this mean?

27. What it means…
heavier objects require more force to
move the same distance as lighter
objects.

28. Newton’s Third Law of Motion
For every
action there is
an equal and
opposite re-
action.

29. What it means
whenever an object pushes another
object it gets pushed back in the
opposite direction equally hard.

30. Example 2
The rocket's action is to push down on the
ground with the force of its powerful
engines, and the reaction is that the
ground pushes the rocket upwards with
an equal force.

31. Reminder: Work is…
Work: remember that for work to be done
the object must move in the same
direction as the force.
Work (W) = Force (F) x distance (d)
W = Fd

32. Balanced or Unbalanced Forces

40. Example questions - balanced
and unbalanced forces
Formula 1 car accelerating from the starting
grid
A cyclist braking
A satellite orbiting the Earth at constant
speed
A person resting in an armchair
A taxi travelling at a constant speed on
straight road
.

41. Work Force Distance
Use the formula for Work to fill in the
table – glue the table in your journal