conservation and dissipation of energy
,conservation and dissipation of energy
P1: Conservation and Dissipation of Energy
1.1 Changes in Energy Stores — Study Notes
Learning Objectives
You should be able to:
● Describe the different ways energy can be stored
● Explain how energy is transferred
● Describe energy changes when an object falls
● Explain energy transfers when a falling object hits the ground (without bouncing)
Energy Stores
Energy can be stored in different ways:
● Chemical energy store
○ Found in fuels, food, and batteries
○ Energy is transferred during chemical reactions
● Kinetic energy store
○ Energy an object has because it is moving
● Gravitational potential energy (GPE) store
○ Energy stored due to an object’s position above the ground
● Elastic potential energy store
○ Energy stored when an object is stretched or squashed (e.g. a spring)
● Thermal energy store
○ Energy a substance has because of its temperature
Energy Transfers
Energy can be transferred:
● By heating
● By waves (e.g. sound or light waves)
● By an electric current
● By a force moving an object
,Falling Objects
● When an object is thrown upwards:
○ Kinetic energy decreases
○ Gravitational potential energy increases
● When an object falls freely:
○ Gravitational potential energy decreases
○ Kinetic energy increases
● When a falling object hits the ground and does not bounce:
○ Kinetic energy decreases to zero
○ Energy is transferred to:
■ The thermal energy store of the object and surroundings (main
transfer)
■ Sound waves (small amount of energy)
Examples of Energy Transfers
Torch
● Chemical energy store (battery)
→ energy transferred by electric current
→ light emitted and thermal energy of bulb and surroundings increases
Electric Heater / Kettle
● Electrical energy transferred by current
→ thermal energy store of the heater/water increases
Electric Train
● Energy transferred by electric current from power station
Moving up a hill at constant speed:
● Kinetic energy store stays the same
● Gravitational potential energy store increases
Braking to a halt:
● Kinetic energy store decreases
● Energy transferred to thermal energy stores of brakes and surroundings
Microwave Oven
, ● Electrical energy transferred by current
→ energy transferred by waves (microwaves)
→ thermal energy store of the food increases
Key Points (Exam Summary)
● Energy is stored in different energy stores
● Energy is transferred, not created or destroyed
● Falling objects:
○ GPE ↓, KE ↑
● On impact (no bounce):
○ KE ↓
○ Thermal energy of surroundings ↑
○ Some energy transferred by sound waves
P1.2 Conservation of Energy — Study Notes
Learning Objectives
You should be able to:
● Define conservation of energy
● Explain why conservation of energy is important
● Describe what a closed system is
● Describe changes to energy stores in a closed system
Conservation of Energy
Principle of conservation of energy:
Energy cannot be created or destroyed.
It can only be transferred between energy stores.
This applies to all energy changes.
Systems and Closed Systems
● A system is an object or a group of objects.
,conservation and dissipation of energy
P1: Conservation and Dissipation of Energy
1.1 Changes in Energy Stores — Study Notes
Learning Objectives
You should be able to:
● Describe the different ways energy can be stored
● Explain how energy is transferred
● Describe energy changes when an object falls
● Explain energy transfers when a falling object hits the ground (without bouncing)
Energy Stores
Energy can be stored in different ways:
● Chemical energy store
○ Found in fuels, food, and batteries
○ Energy is transferred during chemical reactions
● Kinetic energy store
○ Energy an object has because it is moving
● Gravitational potential energy (GPE) store
○ Energy stored due to an object’s position above the ground
● Elastic potential energy store
○ Energy stored when an object is stretched or squashed (e.g. a spring)
● Thermal energy store
○ Energy a substance has because of its temperature
Energy Transfers
Energy can be transferred:
● By heating
● By waves (e.g. sound or light waves)
● By an electric current
● By a force moving an object
,Falling Objects
● When an object is thrown upwards:
○ Kinetic energy decreases
○ Gravitational potential energy increases
● When an object falls freely:
○ Gravitational potential energy decreases
○ Kinetic energy increases
● When a falling object hits the ground and does not bounce:
○ Kinetic energy decreases to zero
○ Energy is transferred to:
■ The thermal energy store of the object and surroundings (main
transfer)
■ Sound waves (small amount of energy)
Examples of Energy Transfers
Torch
● Chemical energy store (battery)
→ energy transferred by electric current
→ light emitted and thermal energy of bulb and surroundings increases
Electric Heater / Kettle
● Electrical energy transferred by current
→ thermal energy store of the heater/water increases
Electric Train
● Energy transferred by electric current from power station
Moving up a hill at constant speed:
● Kinetic energy store stays the same
● Gravitational potential energy store increases
Braking to a halt:
● Kinetic energy store decreases
● Energy transferred to thermal energy stores of brakes and surroundings
Microwave Oven
, ● Electrical energy transferred by current
→ energy transferred by waves (microwaves)
→ thermal energy store of the food increases
Key Points (Exam Summary)
● Energy is stored in different energy stores
● Energy is transferred, not created or destroyed
● Falling objects:
○ GPE ↓, KE ↑
● On impact (no bounce):
○ KE ↓
○ Thermal energy of surroundings ↑
○ Some energy transferred by sound waves
P1.2 Conservation of Energy — Study Notes
Learning Objectives
You should be able to:
● Define conservation of energy
● Explain why conservation of energy is important
● Describe what a closed system is
● Describe changes to energy stores in a closed system
Conservation of Energy
Principle of conservation of energy:
Energy cannot be created or destroyed.
It can only be transferred between energy stores.
This applies to all energy changes.
Systems and Closed Systems
● A system is an object or a group of objects.
