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

frame of reference

The object used for comparing another object to describe its position is called a…

Describe Frame of Reference

Name the frame of reference in each of the following

statements.

The dog is beside the house.

The duck is swimming in the pond.

You can tell that an object has moved when its __________ has changed.

position

Motion happens when an object changes position.

Describe Motion

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

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

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

What is the formula for calculating speed?

Speed is calculated by dividing distance by time –

Calculate This SpeedA 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?

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 sSpeed = 5m/s

Remember to include

the UNITS!!

A ______ graph can be used to show the change in an object’s speed over time.

line

Distance Time Graphs

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.

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.

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.

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!

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.

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.

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!

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

Unbalanced ______ cause changes in motion.

forces

Describing Forces

What is a force?

• A force is push

• or a pull

• Force is measured in Newtons

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.

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

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.

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

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

You Try It: Calculating Net Force

How did you do???

To decrease the amount of force needed to do something. and / or make work seem easier we use ________________.Simple machines

Pulleys

A pulley wheel is a mechanism which helps move or lift objects.

pulley

Exercise machine

100 ft

100 lbs 100 lbs

100 lbs

100 lbs

Single PulleySingle 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.

Movable PulleyMovable 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

Movable PulleyMovable Pulley

http://www.swe.org/iac/LP/pulley_03.html

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.

Combined (double) Combined (double) PulleyPulley:

•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.

COMBINED PULLEYCOMBINED PULLEY

Whether it is being pushed or pulled, moving or still, all things have ______.energy

The energy of motion is __________ energy.

kinetic

The energy of position is _____________ energy.

potential

Name the type of energy in each of

the following statements.

The ball is rolling down the hill.

The roller coaster is sitting at the top of the track.

The pencil fell off the edge of the desk.

The skier is at the top of the ski jump.