Reassessment Review For Unit 9

1

• Reassessment Review For Unit 9 10
• To view the presentation property click
  Slideshow and From Beginning
• As you go through the presentationcomplete the
  activities and , take detailed notes on the
  following topics.
• Measuring motion Including Speed
• Reading Motion Graphs
• Forces
• Potential Kinetic Energy
• Pulleys
• Inclined Planes

2
Measuring MOTION
3
Describe Frame of Reference
The object used for comparing another object to
describe its position is called a
frame of reference
4
Name the frame of reference in each of the
following statements.
5
The dog is beside the house.
house
6
The duck is swimming in the pond.
pond
7
Describe Motion
You can tell that an object has moved when its
__________ has changed.
position
Motion happens when an object changes position.
8
Describe Acceleration

• A change in velocity which may be
• A change in speed
• Starting
• Stopping
• Speeding up
• Slowing down
• A change in direction
• Acceleration is caused by unbalanced forces

9
The distance an object moves in a certain amount
of time is called _________.
speed
10
Describe Speed

• A way to describe motion
• Average speed - calculated by dividing the
  distance traveled by the amount of time it takes
  to travel that distance
• Constant speed - Speed that does not change
• Instantaneous speed - Speed of an object at any
  given time

11
What is the formula for calculating speed?
Speed is calculated by dividing distance by time

12
Calculate This Speed
A football field is about 100 m long. If it takes
a person 20 seconds to run its length, how fast
was the football player running?
13
Calculate this Speed
A football field is about 100 m long. If it takes
a person 20 seconds to run its length, how fast
was the football player running? Speed
Distance Time Speed 100 m 20 s Speed
5m/s
Remember to include the UNITS!!
14
A ______ graph can be used to show the change in
an objects speed over time.
line
15
Distance Time Graphs
Understanding Motion Graphs
16
Distance Time Graphs

• Describing a journey made by an object is not
  exciting if you just use words. As with much of
  science, graphs are more revealing.
• Plotting distance against time can tell you a lot
  about a journey. Let's look at the axes
• Time always runs horizontally (the x-axis). The
  arrow shows the direction of time. The further to
  the right, the longer time from the start.
• Distance runs vertically (the y-axis). The higher
  up the graph we go, the further we are from the
  start.

17
Not moving? This is what it looks like

• If something is not moving, a horizontal line is
  drawn on a distance-time graph.
• Time is increasing to the right, but its distance
  does not change. It is stationary.

18
Moving.

• If something is moving at a constant speed, it
  means we expect the same increase in distance in
  a given time
• Time is increasing to the right, and distance is
  increasing steadily with time. It moves at a
  steady speed.

19
Can you describe what is going on here?

• For the first part of the journey shown by the
  graph below, the object moved at a steady (slow)
  speed.
• It then suddenly increased its speed, covering a
  much larger distance in the same time.
• This sort of motion is not very realistic, but is
  easy to understand. It also makes calculations
  easier!

20
What is the effect of line Steepness or slope?

• Both the lines below show that each object moved
  the same distance, but the steeper yellow line
  got there before the other one
• A steeper gradient indicates a larger distance
  moved in a given time. In other words, higher
  speed.
• Both lines are of constant gradient, so both
  speeds are constant.

21
Speeding Up!

• The line below is curving upwards. This shows an
  increase in speed, since the gradient is getting
  steeper
• In other words, in a given time, the distance the
  object moves is larger. It is accelerating.

22

• There are three parts to the journey shown below
  
• Moving at a steady speed, slowly Not moving for
  quite some time Moving again, but at higher
  speed
• In all the graphs so far, we have not seen any
  numbers - it's about time we did!

23
Calculate the speeds within a graph

• Stage 1 speed distance / time 150 m 30
  s 5 m/s
• Stage 2 speed distance / time 100 m 10
  s 10 m/s
• Stage 3 speed distance / time 100 m 50
  s 2 m/s

24
Unbalanced ______ cause changes in motion.
forces
25
What Are Forces ?
26
Describing Forces
What is a force?

• A force is push
• or a pull
• Force is measured in Newtons

27
Combining forces

• Usually, more than one force is exerted on an
  object at the same time.
• The sum of all forces acting on an object is
  called the net force.
• You need to look at the net force in order to
  figure out if or how an object will move.

28
Balanced Forces

• Net force zero
• No change in motion
• (object is not moving)
• List 3 examples of balanced forces
• Paper on desk
• You in the chair
• Flag not moving

29
Unbalanced Forces

• There is a net force acting on an object.
• Causes a change in motion
• Possible to add the forces together to find the
  size direction of the net force.

30
Unbalanced forces

• If the forces are moving in the same direction,
  add the forces.
• Example
• Girl pushes 25 N to the right
• Boy pulls 20 N to the right
• Net Force 45 N to the right
• The piano moves to the right

31
Unbalanced forces

• If the forces are moving in opposite directions,
  subtract the forces.
• Example
• Dog 1 pulls 10 N to the left
• Dog 2 pulls 12 N to the right
• Net Force 2 N to the right

32
(No Transcript)
33
You Try It Calculating Net Force
34
How did you do???
35
To decrease the amount of force needed to do
something. and / or make work seem easier we use
________________.
Simple machines
36
Pulleys Inclined planes
37
Pulleys
A pulley wheel is a mechanism which helps move or
lift objects.
pulley
Exercise machine
38
Single Pulley

• Changes the direction of the force needed to lift
  something, but NOT mechanical advantage.
• It just feels easier to pull down than to pull up.

39
Movable Pulley

• Movable Pulley
• Pulley moves along the rope
• Wheel supports the load
• Effort to lift is in the same direction as
  movement
• REDUCES the forces needed to move an object

40
In the second picture, the weight is held by two
ropes instead of one. That means the weight is
split equally between the two ropes, so each one
holds only half the weight.
http//www.swe.org/iac/LP/pulley_03.html
41
COMBINED PULLEY

• Combined (double) Pulley
• Has at least two wheels
• The more complex the pulley, the less the effort
  needed to lift the object.
• The main disadvantage is it travels a very long
  distance.

42
Whether it is being pushed or pulled, moving or
still, all things have ______.
energy
43
Potential Vs Kinetic Energy
44
The energy of motion is __________ energy.
kinetic
45
The energy of position is _____________ energy.
potential
46
Name the type of energy in each of the following
statements.
47
The ball is rolling down the hill.
KINETIC
48
The roller coaster is sitting at the top of the
track.
POTENTIAL
49
The pencil fell off the edge of the desk.
KINETIC
50
The skier is at the top of the ski jump.
POTENTIAL
51
You Did it!