Mass and weight

The mass of an object is the amount of matter it contains and is measured in kilograms (kg). The weight of an object is the size of gravitational attraction between the object and the planet (or moon) it is on. We measure weight in Newton (N).
The table below gives some examples of the masses and weights of different objects on the Earth and on the Moon.
We can see from this table that gravity on the Moon’s surface is only 1/6th of that on the Earth. So objects here only weigh 1/6th of what they would weigh on Earth. The masses of all the objects do not change. They are the same here on the Earth as they are on the Moon.
Working out weight
Weight depends on how much mass an object has. It also depends on the strength of gravity.
We say that the strength of the Earth’s gravity is 10 Newton per kilogram (10N/kg). We call this the Earth’s gravitational field strength. We can work out the weight of an object as follows.
Weight = mass x gravitational field strength
(Newton, N) (Kilograms, kg) (Newton/kilogram, N/kg)

E-Activity 5

How can a helicopter hover?
1-When people are lifted from a boat; the helicopter has to keep very still. This is difficult because the weight of the helicopter is always pulling it downwards.
(a) What force is acting upwards on the helicopter?
(b) Explain how the helicopter can keep still.

2-What would happen to the helicopter if
(a) The uplift was greater than the weight?
(b) The weight was greater than the uplift?
Give reasons for your answers.

3-Find the resultant force (the forces all act along the same line)

Applying forces

Equal and opposite
When two objects interact, there are always two forces. The forces are equal in size and opposite in direction. One force acts on one object and an equal and opposite force acts on the second object.

More than one force
The horse in the first diagram is pulling the tree trunk with a 1000 N force.
In the second diagram, two horses are pulling. Their forces are in the same direction so they add together. They have the same effect as if a single force equal to both the forces added together was acting.

Forces that balance
In this diagram, the horses pull with forces that are equal in size but in opposite directions.
The forces cancel each other out.

Balanced and unbalanced forces

In everyday life it is rare for an object to be acted upon by no forces or a single force. It is much more likely that it will experience several forces. These forces may be balanced or unbalanced.
If the two tug of war teams in figure pull with the same force, the forces are balanced and there is no movement. (Figure 1)
If one of the teams pulls with a force which is greater than that of the opposition, the forces are unbalanced and there is movement. (Figure 2)
The ship above is floating in water and is stationary. There are several forces acting upon it, so these forces must be balanced.
Gravitational forces, i.e. the weight of the ship, are pulling it downwards but a second force called the up thrust from the water is pushing upwards. (Figure 3)
If too much cargo is loaded onto the ship, the weight may become larger than the up thrust and the ship may sink.
An object placed on a table also experiences balanced forces. (Figure 4)
If an object is moving and balanced forces are applied to it, the object will continue to move in the same direction and at the same speed. The aero plane below is experiencing four forces. Its weight, a lifting force from its wings, thrust from its engines driving it forwards and drag from the air trying to resist the forward motion. (Figure 5)
If the lift and weight forces are balanced, there is no vertical motion. The aero plane stays at the same height.
If the thrust and drag forces are balanced, the aero plane will travel at a constant speed in a straight line.

5-Effects of forces

There are many different types of force. These include pushes, pulls, twists and stretches.
If you apply a force to an object it may:
• Make it start to move
• Make it move faster
• Slow it down
• Make it stop
• Change the direction in which it is moving
• Change its shape

Sometimes it is not necessary to be in contact with an object in order to apply a force to it.
The steel nails in figure are lifted by a force. This attractive force exists between magnets and magnetic materials such as iron and steel.
The bungee jumper in figure has just jumped out of the basket and is feeling the force of gravity pulling him downwards. The common name given to this force is weight.
There are gravitational forces between all objects, but they are often very weak. They are only noticeable when one or both of them are massive, such as a planet, moon or star. It is gravitational forces of attraction that hold the Moon in orbit around the Earth and hold the planets in orbit around the Sun.

E-Activity 4

1-
(a) Make a copy of the graph (Example 1) but mark the changes for part C instead of part B.
(b) Calculate the speed for part C of the graph. Show your working.
2-
(a) Make a copy of the graph (Example 2) but mark the changes for part R instead of part Q.
(b) Calculate the acceleration for part R of the graph. Show your working.
3-
(a) Make a copy of the graph (Example 3). Mark the area under the graph for between 5 and 10 seconds. Then calculate the distance traveled during this period. Show your working.
(b) Find the total distance traveled by the object between 0 and 15 seconds.

4-More about motion graphs

Calculating speed from a distance-time graph
Speed = distance/time
So, for part A of the graph, speed=20m÷5s=4m/s
To calculate the speed for other parts of the graph, you need to use the slope o0r gradient of the graph.
Example 1 shows you how to do this for part B of the graph.

Calculating acceleration from velocity-time graph
Acceleration=change in velocity/time taken
So, for part P of the graph, acceleration=2m/s÷2s=1m/s2
To calculate the acceleration for other parts of the graph, you need to use the slope or gradient of the graph.
Example 2 shows you how to do this for part Q of the graph.

Calculating distance traveled from a velocity-time graph
The area beneath a velocity-time graph tells you the distance that an object has traveled.
Example 3 shows how you can work out from the graph the distance traveled in the first 5 seconds.

E-Activity 3

Rocket launch

1-The data in the table are for a rocket launch.
(a) Plot a velocity-time graph for the rocket as it lifts off.
(b) how does the velocity-time graph show the rocket is accelerating as it leaves the launch pad?
(c) Draw a line of best fit through the points. Measure the gradient of this line to find the rocket's acceleration.

Performance figures

2-Two sports cars are tested against each other from a standing start.
Look at their velocity-time graphs.
(a) Which car accelerates more quickly to 60 mph?
(b) Which car has the greater top speed?
(c) Which car decelerates faster when it brakes?
Give reasons for your answers.

3-velocity-time graphs

The figure shows three cars moving in different ways. The velocity-time graph for each car is shown as well.
1-What does a horizontal line on a velocity-time graph tell you about the velocity?
2-What feature of a velocity-time graph tells you that the object is accelerating?
3-The velcity-time graph for an object is a horizontal line through the origin. What can you say about the object's motion?
Velocity-time graphs look very similar to distance-time graphs but beware, they are quite different. Do not confuse the two.

A cyclist's journey

A cyclist is riding along a straight road. Look at the velocity-time graph for the cyclist. The slopeof the velocity-time graph tells you how the velocity is changing.
1-In which parts of the journey is the velocity steady?
2-What is the cyclist's velocity
(a) in section A?
(b) in section C?
3-How does the graph show an acceleration?
4-How does the graph show that the cyclist slows down quicker than she speeds up?
A steeper slope on a velocity-time graph means a bigger acceleration (or deceleration)

E-Activity 2

1-Look at the aircraft flying in a circle.
(a) Is its speed constant?
(b) Is its velocity constant?
Give a reason for your answers.

2-Calculate the change of velocity for each of the examples in the figure.

3-Look at the examples in the picture and work out the missing items in each one.

2-Velocity and Acceleration

Same speed but different velocity
The diagram shows three aircraft taking part in a display.
1. What is the same about the motion of the planes?
2. What is different?
All three aircraft have the same speed, but they are moving in different directions. We say that they have differnt velocities. Velocity is speed in a given direction.
Acceleration
When your velocity changes, we say that you accelerate. Racing drivers want a very large acceleration. This means they want to go from a low speed to a high speed in a very short time.
How to calculate acceleration
The racing car in the figure takes 5 seconds to reach a velocity of 50 metres per second. So every second, its velocity increases by 10 metres per second. This is its acceleration. You can work out acceleration like this:
acceleration = change in velocity/time taken
So for the racing car, acceleration = 50m/s / 5s = 10m/s2
The change in velocity is measured in metres per second. the time taken is measured in seconds. So the units of acceleration are metres per second, per second.

E-Activity 1

This example shows how we can describe a journey on a distance-time graph. Look at it carefully and use it to answer the questions.

1. Look at stage I of the journey, when Jane is walking.
a. How many metres does Jane walk?
b. How long does it take Jane to walk this distance?
c. What is her speed for this part of her journey?

2. Look at stage II of the journey.
a. What is Jane's speed while she chats?
b. Describe the shape of the graph for this stage.
c. Write down a rule for telling when something is stationary on a distance-time graph.

3.
a. Which part of the graph is steeper, I or III?
b. Which stage of the journey is faster, I or III?
c. What is the connection between speed and slope on a distance-time graph?

The slope of a distance-time graph tells you about the speed.
If the object is stationary, the graph is a horizontal line.
If the object has a higher speed, the graph has a steeper slope.

A distance-time graph

A man is running at a steady speed in a straight line. This graph shows the distance he travels against time taken, so it is called a distance-time graph.
You can read from the graph the distance he travels in a period of time. For example, it takes him 4 seconds to run 20 metres.
What speed is this?

1-Travelling at speed

Calculating speed:
A sprinter runs 10 metres in 1 second. His speed is 10 metres per second (m/s). Speed in metres per second tells you how many metres you travel in 1 second.
You can work out speed like this:
speed (metres persecond) = distance travelled (metres)÷ time taken (seconds)

Example:
On a motoway, a car travels 300 metres in 10 seconds.
Distance traveled = 300 metres (m)
Time taken = 10 seconds (s)
Speed = ?
So speed = 300 m ÷ 10s= 30 metres per second (m/s)

INTRODUCTION

Since the aim is to integrate ICT with Physics, it is important to note that the focus will be on the application of various tools and technologies in teaching and learning. As such we expect that you are a competent user of commonly used tools, such as a word processor, spreadsheet, presentation software, web browsers, e-mailing and so on, and will be able to learn other tools quite easily.


The course will be taught by e-learning approaches through Online-Learning will be a process of constructing personal meaning through interation with the content, tutor and peers, and reflection on these interactions.


A large part of your study will be independent. You will be able to interact with tutors and peers through e-mail and e-activities on Online. Participation in e-activities is an integral part of learning in this course. Throughout the term there will be different types of activities to help you deepen your understanding, reflect on new ideas and apply new knowledge and skills to practical examples.


It is hoped that this will make the learning of Physics at this level more interesting and exciting and will give a good foundation for higher learning.