IGCSE Coordinate Science 1P3: Energy, Work, and Power

Unit 7 – part 1

Work

• Work – the force on an object and the object should move a certain distance in the direction of the force

W = FdWhere:– W is work measured in J (joules)– F is force measured in N (newtons)– d is distance measured in m (meters)

Examples

• 1. A force of 20N makes the object move 4.8m in the direction of the force. Calculate the work done on the object.

Examples2. A 5kg box is on the floor. It takes a force of 50N to move it to the right a distance of 3m.• a) Calculate the work done to move the box

horizontally .• b) Calculate the work done to move the box

vertically at a height of 2m.

Energy

• Energy – ability to do work.

Work done = Energy transferred

Forms of Energy

• 1) Gravitational Potential Energy – stored energy with respect to position or at a certain height.

• 2) Kinetic Energy – energy of moving objects.

Forms of Energy

• 3) Elastic Potential Energy – stored energy in springs or any elastic material. Also known as strain energy.

• 4) Chemical Energy – energy stored in the chemical bonds of food and other fuel.

Forms of Energy

• 5) Thermal Energy (or Heat) – energy transfer from hot to cold objects.

• 6) Nuclear Energy – energy released when the nucleus of an atom splits or fuses.

• 7) Electrical Energy – energy of an electric current.

• 8) Light Energy• 9) Sound Energy

Energy Transformations

• Example

Energy Transfer Diagram

The Principle of Conservation of Energy

• “Energy cannot be created or destroyed but is changed from one form to another.”

Now it’s your turn…

Kinetic Energy

• Kinetic Energy – energy of moving objects

KE = (1/2)mv2

Where:– KE is kinetic energy measured in J (joules)– m is mass measured in kg– v is velocity measured in m/s

• NOTE: remember that velocity is squared!

Gravitational Potential Energy

• Gravitational Potential Energy – stored energy with respect to position.

PE = mghWhere:– PE is gravitational potential energy measured in J– m is mass measured in kg– g is acceleration due to gravity (9.8 m/s2)– h is height measured in m

Examples1. Galileo drops a 1kg metal ball from the leaning tower of Pisa, which is 45m high.• a) Calculate the potential energy of the ball

just before dropping.• b) Calculate the speed of the

metal ball just before reaching the ground.

Helpful Website

• http://phet.colorado.edu/en/simulation/energy-skate-park

Efficiency

• Efficiency – the fraction (or percentage) of energy that is converted into a useful form.

Examples• 1. Below is the energy transfer diagram of a

light bulb. Calculate its efficiency.

Examples

• 2. A coal-fired power station produces 100 MJ of electrical energy when it is supplied with 400 MJ of energy from its fuel. Calculate its efficiency.

• 3. A lamp is 10% efficient. How much electrical energy must be supplied to the lamp each second if it produces 20 J of light per second?

Power

• Power – rate at which energy is transferred, or rate at which work is done.

P = E / tWhere:– P is power measured in W (watts)– E is energy or work measured in J (joules)– t is time measured in s (seconds)

Examples

• A crane lifts an object of weight 400N through a vertical distance of 2.5m in 5.0s. Calculate:

• a) the gain in gravitational potential energy.• b) the output power of the crane.