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Conservation of Energy

Learning objectives:

State the principle of conservation of energy
Apply calculations to determine energy changes in closed systems.
Analyze energy losses by examining or investigating open systems.

Key Vocabulary:

Kinetic energy

Gravitational potential energy

Thermal energy

Starter 1

A spring of mass with a spring constant of 10N/kg is extended 0.19m. Calculate its elastic potential energy.

Starter 2

A spring is stretched 500 cm and has a kinetic energy of 5.8 J. Calculate the spring constant.

Starter 3

What is meant by “conservation of energy?”

Challenge:

Is energy always conserved? How do you know? Give an Example

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Conservation of Energy

Learning objectives:

State the principle of conservation of energy
Apply calculations to determine energy changes in closed systems.
Analyze energy losses by examining or investigating open systems.

Key Vocabulary:

Kinetic energy

Gravitational potential energy

Thermal energy

Starter 1

E=½ kx²

E=1/2×10×(0.18)²

^=0.185

Starter 2

k=2E/x².

2(5.8)/(5)²

⁼

^0.0116

Starter 3

Energy is not created or destroyed

Challenge:

Is energy always conserved? How do you know? Example

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What is Energy Conservation?

Energy conservation means using less energy by being more efficient.
It is based on the principle that energy cannot be created or destroyed, only transformed.

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Energy cannot be

created or destroyed.

It is ALWAYS conserved

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Kinetic Energy: The Basics

Kinetic energy is the energy of motion.
The formula for kinetic energy (KE) is: KE = 1/2 mv², where m is mass and v is velocity.
Can you think of examples of objects that have kinetic energy?

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Calculating Kinetic Energy

To calculate kinetic energy, you need the mass and velocity of an object.
Example: What is the kinetic energy of A car with a mass of 1000 kg moving at 20 m/s.?

KE = 1/2 (1000 kg)(20 m/s)² = 200,000 J (Joules).
What would happen to the kinetic energy if the speed doubled?

Challenge: A car with a mass of 1,500 kg has 300,000 J of kinetic energy. What is its speed?

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More Calculation Examples

Example 1: A bicycle with a mass of 15 kg traveling at 5 m/s.

KE = 1/2 (15 kg)(5 m/s)² = 187.5 J.

Example 2: A soccer ball with a mass of 0.5 kg kicked at 10 m/s.

KE = 1/2 (0.5 kg)(10 m/s)² = 25 J.
Stretch: How do these examples compare to the car's in the image’s kinetic energy? Why do think this is?

Challenge: A cyclist doubles their speed from 5 m/s to 10 m/s. By what factor does their kinetic energy increase?

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GPE=Kinetic

https://www.pbslearningmedia.org/resource/hew06.sci.phys.maf.rollercoaster/energy-in-a-roller-coaster-ride/

Calculate the gravitational potential energy at point W?
What is the kinetic energy at point X?

The mass of the car is 800kg

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^{GPE: mgh = 800(1)(12) =}

^{KE=½ mv2 =½ (800)(20)^2 =160000}

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Is this the case in real life?

Energy is wasted in every system.

This is usually in the form of heat and sometimes as sound or light.

What happens to this energy?

Wasted energy is dissipated (spread out) into the surroundings.

This heats the surroundings up

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Examples of Wasted Energy

Leaving lights on when not needed.
Inefficient appliances that consume more energy than necessary.
Cars idling instead of turning off the engine.
What strategies can you think of to reduce wasted energy in your daily life?

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Which scooter will be the cheapest to run? Explain why.

Assuming the same size battery, which scooter will have the greatest range? Explain why.

Which scooter will have the greatest top speed? Explain your answer.

Electrical Appliances

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LO: Understand the different ways that electricity can be transferred to different energy stores.

Apply skills to exam style questions.

Describe energy transfers in real life systems

Identify the different ways that electrical appliances can transfer energy.