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## Acceleration depends on both mass and the net force

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### Acceleration depends on both mass and the net force Newton s 2nd law: The acceleration produced by a net force on a body is directly proportional to the magnitude ... – PowerPoint PPT presentation

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Title: Acceleration depends on both mass and the net force

1
Acceleration depends on both mass and the net
force
• Newtons 2nd law
• The acceleration produced by a net force on a
body is directly proportional to the magnitude of
the net force.
• It is in the same direction as the net force, and
is inversely proportional to the mass of the
body.

2
Acceleration depends on both mass and the net
force

3
If the net force is zero, there is no
acceleration
4
If the net force is not zero, there is
acceleration
5
Acceleration depends on net force
• A force of 10N accelerates the box

6
Acceleration depends on net force
• A force of 20N accelerates the box twice as fast

7
Acceleration depends on mass
• A force of 10N accelerates the box

8
Acceleration depends on mass
• A force of 10N accelerates the smaller box faster

9
• An airplane weighs 2,000,000N and needs to
accelerate at 4m/s2. What thrust (force) must
the engines produce?

10
• A train engine has a mass of 120,000kg and pulls
a 75,000kg car. The train can pull with a force
of 585,000N. What is its maximum acceleration?

11
• Now suppose a second car is added to the train in
the last problem. What is the new maximum
acceleration?
• A train engine mass 120,000kg
• Train car1 75,000kg.
• Train car2 75,000kg.

12
In order for sink a ship in the harbor, a cannon
ball of 25kg must be accelerated at 44m/s2. How
much force is required to hit the ship?
13
• A stunt penguin want to fly around the room and
needs to accelerate enough to compensate for
gravity.
• If his thruster can produce 88N of force, what is
the maximum mass of the penguin and his thruster?

14
Elephant feather
without air resistance
Elephant feather
with air resistance
15
(No Transcript)
16
Friction
• Friction is a force like any other force
• Friction acts on materials that are in contact
with each other
• Friction slows down motion
• Forces due to friction are always in the opposite
direction of the motion.

17
Find the net force
18
Free-body diagrams
• Draw the free-body diagram for a book is at rest
on a table top.

19
• A girl is suspended motionless from a bar which
hangs from the ceiling by two ropes. A free-body
diagram for this situation looks like this

20
• An egg is free-falling from a nest in a tree.
Neglect air resistance. A free-body diagram for
this situation looks like this

21
• A rightward force is applied to a book in order
to move it across a desk at constant velocity.
Consider frictional forces. Neglect air
resistance. A free-body diagram for this
situation looks like this

22
• A college student rests a backpack upon his
shoulder. The pack is suspended motionless by one
strap from one shoulder. A free-body diagram for
this situation looks like this

23
• A skydiver is descending with a constant
velocity. Consider air resistance. A free-body
diagram for this situation looks like this

24
• A force is applied to the right to drag a sled
across loosely-packed snow with a rightward
acceleration. A free-boy diagram for this
situation looks like this

25
• A football is moving upwards towards its peak
after having been booted by the punter. A
free-body diagram for this situation looks like
this

26
• A car is coasting to the right and slowing down.
A free-body diagram for this situation looks like
this

27
Net Force
• If there is no movement
• The net force is zero
• If there is no acceleration
• The net force is zero
• If there is acceleration
• The net force is not zero.

28
Free Body diagrams
• If the net forces are zero, the FBD is balanced

29
Examples of zero net force?
• A book on a desk
• A sky diver with a parachute open
• A bike moving at a constant speed.

30
Free Body diagrams
• If the net forces are NOT zero, the FBD is NOT
balanced

31
Free Body diagrams
• If the net forces are NOT zero, the FBD is NOT
balanced

Fapp
Ffric
32
Examples of non zero net force
• A book sliding across a desk
• A sky diver falling without a parachute

33
Pressure
• P pressure (units are pascals Pa)
• P F/A
• A Area
• F Force

34
Pressure
35
Hydraulic Pressure
Hydraulic Lift
36
Pressure
• Does a books weight change depending on the
angle it is held at?
• No Wmg
• Does the pressure exerted by a book change
depending on the angle it is held at?
• Yes

37
Pressure
• What is the difference between weight and
pressure?
• Weight is measured in N
• Pressure is N / Area
• PF/A
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