Lesson 1 :

Resources & Forms of Energy

Lesson 2:

Energy Transformation

Lesson 3:

Heat Energy

1. Fuel is burnt in the car to produce energy which moves the car.

2. Food is the living organism’s fuel. Food is burnt in the body to get energy needed for vital activities.

3. Energy is the ability to do work or make a change.

4. A body which is moving has kinetic energy.

5. Raise a book & put it on a high shelf. Your energy is stored in the book. The stored energy is potential energy. When the book falls down, its potential energy is converted into kinetic energy.

Kinetic energy is energy due to motion. Potential energy is the energy stored in an object due to its height. Mechanical energy is the sum of kinetic energy & potential energy.

Mechanical energy = potential energy only.

Mechanical energy of the ball at B = Mechanical energy only.

Potential energy increases when the object’s weight or height increase.

Potential energy = weight x height.

Example: compare the potential energy of 2 balls, the weight of each is 1 Newton & the first is placed at a height of 1m & the 2^nd is placed at a height of 2 m.

Solution:

Potential energy (1) = 1 Newton x 1 m

= 1 Joule

Potential energy (2) = 1 Newton x 2 m

= 2 Joules

Potential energy of the 2^nd object is double the potential energy of the 1^st object.

Kinetic energy increases if the mass or the speed of the moving object increase.

T he following rule calculates kinetic energy .

A solved example:

Calculate the kinetic energy of a ball that has

a mass =0.5 kg & moves with a speed 3 m/s.

Solution:

Kinetic energy = ½ x 0.5 x (3)²

= 2.25 Joules.

1. Choose the correct answer:

1. An object of 20 N weight is placed on a shelf of height 5 m. its potential energy = …….J

(50 – 100 – 150)

2. A truck & a car move with the same speed. The car has ……………kinetic energy than/ as truck.

(less – more – the same)

3. The …………………..energy of water at the top of waterfalls is maximum.

(kinetic – potential – mechanical)

4. T he kinetic energy of a falling ball……………………gradually.

(doesn’t change – increases – decreases)

5. An object is thrown upwards, therefore its velocity……………...

(increases – decreases – doesn’t change)

2. Solve the following problems:

1. Calculate the mechanical energy of a book whose weight = 10 Newton & is placed on a shelf 3m high.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

2. Calculate the mechanical energy of a ball of weight 3 Newton , its mass = 0.3 kg , it’s thrown up with speed 3 m/s to a height 4m.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

A pendulum is a ball tied with a string & fixed at a point. When the ball is pushed, it moves to the right & then back to the beginning point, then to the left.

A B

At points A&B , the potential energy of the pendulum is maximum.

As it moves away from point A, its energy is changed to kinetic energy.

The mechanical energy of the pendulum is the same at each point.

Forms of energy:

Forms of energy	Sun
Light	Sun
Sound	Bell – Piano
Chemical	Fuel – Battery – Food
Heat	Heater
Kinetic	A moving car – wind
Potential	Stretched bow to through an arrow
Electric	Produced by an electric generator
Nuclear	Released by a nuclear bomb

Activity 1:

Simple cell

1. In a glass beaker, put 2 metal plates separately (zinc & copper).

2. Fill half the beaker with diluted acid.

3. Connect the 2 plates externally with an electric current.

4. Put a voltammeter in the circuit to measure the electric current.

• Observation :

The pointer of the voltammeter moves to indicate the electric current is passing through the circuit.

• Conclusion:

Chemical energy in the simple cell is transformed into electric energy.

Activity 2:

Prepare an electric circuit like the one in the figure, close the circuit using the switch , open the circuit using the switch.

• Observation :

The bulb light up when the circuit is closed. The bulb is turned off when the circuit is open & electricity isn’t passing in the circuit.

• Conclusion:

In the electric bulb (lamp) electric energy is converted into light energy.

Energy is transformed from one form to another as in the following table.

Device	Energy used	Energy produced
Electric bell	Electric	Sound
Burning fuel in a car	Chemical	Mechanical & heat
Electric generator (dynamo)	Mechanical(kinetic)	Electric
Radio	Electric	S ound
Electric heater	Electric	Heat

Modern technology has many harms, some are mentioned in the following table.

Technology	Harms
Transportation vehicles	Their exhaust pollutes the air. Breathing polluted air harms humans’ health .
Chemical pesticides	They are sprayed to kill harmful insects but harm useful ones as well. They also pollute the air.
Nuclear weapons used in war.	Spread harmful radiations that harm humans’ health. Kill a large number of humans.
Cell phone transmission towers.	Their effect on health is being studied .

Nuclear weapons