1. Force
Work and
Power

2. Formula for Force
Force = Mass * Acceleration

3. Force – push or pull
• a force always acts in a certain
direction
• metric unit of force (N)
ex. if you push something, the force is in
the direction of the push

4. Mass
How much matter is in an object
Measured in grams (g) or Kilograms (kg)

5. Acceleration
Change in Speed
Measured in meters per second squared
(m/s2)

6. Force examples
Weight is a force
Why is weight a force?
Name 3 other forces in your life.

7. Forces in Nature
• Electric force
– ex. lightning
• Magnetic force
– ex. magnetic poles
• Gravity

8. What is gravity?
• The force that attracts a body toward the
center of the earth, or toward any other
physical body having mass
• Sir Isaac Newton
– 1642 – 1727
– The Principia

9. Gravity
• the greater the distance between two
objects, the smaller the gravitational
force
– the force of gravity decreases by the
amount equal to one divided by the
distance (d) squared
• 1/d2

10. What is air resistance?
• air resistance
– force that opposes the movement of an
object in air

11. Air Resistance
• a larger surface area usually results in
greater air resistance
• lighter objects feel more air resistance
than heavier objects

12. Terminal Velocity
• speed at which air resistance and
gravity acting on an object are equal
– as an object falls, it’s speed increases at
a steady rate until it reaches it’s terminal
velocity

13. Vacuum – empty space
• in a vacuum, all objects fall at the
same speed

14. What is friction?
• Friction
– force that opposes the motion of an
object
• the force of friction works in the opposite
direction of the force of motion

15. Types of Friction
• Sliding Friction
– the source of friction is the contact
between two surfaces, at least one of
which is in motion

16. Types of Friction
• Air Resistance
– friction results from air pushing on an
object as it is moving

17. Types of Friction
• Rolling Friction
– friction between two surfaces that are not
in constant contact
• ex. wheels

18. Friction
• friction makes motion possible
• friction also makes it hard to move
objects
• reducing friction makes it easier to
move objects

19. How can friction be reduced?
• by changing sliding friction into rolling
friction
• by using lubricants
– Lubricants – substances that reduce
friction

20. What is pressure?
• Pressure
– force per unit area

21. Pressure
• pressure is the amount of force acting
on a surface
• pressure equals force divided by area
– p = f/a

22. Pressure
• pressure can be changed by changing
the amount of force acting on an area
• pressure can be changed by changing
the area on which a force acts

23. Fluid Pressure
• pressure in gases and liquids

24. Air Pressure
• air pressure is caused by the motion
of particles in the air
• you do not feel the weight of the air
because the pressure inside your
body is equal to the air pressure

25. Air Pressure
• air pressure changes with altitude
– the higher you are, the lower the air
pressure

26. Air Pressure
• Barometer
– instrument used to measure air pressure

27. Water Pressure
• the force of water pressure on an
object is the same in all directions
• water pressure changes with depth
– the deeper you are, the greater the water
pressure

28. Water Pressure
• Manometer
– instrument used to measure pressure in a
liquid

29. What is Bernoulli’s principle?
• Bernoulli’s Principle
– principle that states that as the speed of a
fluid increases, its pressure decreases

30. Bernoulli’s Principle
• airplane wings are designed to use
Bernoulli’s principle
– air traveling over the wings moves faster
than air underneath
– this reduces the pressure on top of the
wing, allowing it to be pushed upward

31. Bernoulli’s Principle
• three forces combine to help an
airplane fly
– the upward force on a plane’s wing is
called lift
– a forward force, or thrust, helps the
plane take off and maintain air speed
– the air resistance on a plane is called
drag

32. Work is the transfer of energy through motion. In
order for work to take place, a force must be exerted
through a distance. The amount of work done
depends on two things: the amount of force exerted
and the distance over which the force is applied.
There are two factors to keep in mind when
deciding when work is being done: something has to
move and the motion must be in the direction of the
applied force.

33. Formula for Work
Work can be calculated by using the
following formula:
Work=force x distance
J = N X m

34. Work is done on the
books when they are
being lifted, but no
work is done on
them when they are
being held or
carried horizontally.

35. Power
Rate at which work is performed or
energy is expended

36. W
P=
t
Power equals Work divided by Time
W = J / s
Watt is the base unit of Power
One watt is equal to 1 joule of
work per second

37. Types of Power
Electrical Power
Uses electrical energy to do work
Mechanical Power
Uses mechanical energy to do work
(linear, rotary)
Fluid Power
Uses energy transferred by liquids
(hydraulic) and gases (pneumatic)