Chapter 1 Conservation And Dissapation Of Energy

Question 1

What energy stores are there?8

Answer 1

• gravitational potential
• electrostatic
• kinetic
• elastic
• magnetic
• thermal
• chemical
• nuclear

Question 2

Gravitational potential def

Answer 2

The energy of an object at height eg. Airplanes, kites, mug on the table

Question 3

Elastic def

Answer 3

When an object is stretched or squashed eg. Inflated balloons, catapult

Question 4

Magnetic def

Answer 4

Repelling poles pushed together, attracting poles pulled apart eg. Compasses, fridge magnets

Question 5

Electrostatic def

Answer 5

Repelling charges have been moved closer, attracting charges have pulled further apart eg. Thunderclouds

Question 6

Kinetic

Answer 6

The energy of a moving object eg. Runners, buses and comets

Question 7

Nuclear

Answer 7

The energy stored in the nucleus of an atom eg. Uranium nuclear power, nuclear reactor

Question 8

Chemical def

Answer 8

Held in chemical bonds. Fuels foods or chemicals found in batteries eg. Foods and muscle

Question 9

Thermal def

Answer 9

Heat energy/temp . Thermal energy can be transferred between objects or from an object to its surroundings eg. Human bodies, hot coffee

Question 10

What is the conservation of energy?

Answer 10

Energy cannot be created or destroyed

Question 11

What does the conservation of energy apply to?

Answer 11

All energy changes

Question 12

What is a closed system

Answer 12

No energy transfers take place out of or into the energy stores of the system. Energy can be transferred between energy in the closed system. The total energy of the system is always the same before and after any transfers

Question 13

What is work?

Answer 13

Work is done on an object when a force makes the object move

Question 14

What does energy transferred equal?

Answer 14

Energy transferred =work done

Question 15

Equation for work

Answer 15

Work done (W) (joules)=force applied (F) (newtons)x distance moved along the line of action of the force (s) (meters’

Question 16

Work and friction

Answer 16

Work done to overcome friction is mainly transferred to thermal energy stores by heating and then to the surroundings

Question 17

What is gravitational potential energy?

Answer 17

Increases when an objects is moved up and decreases when an object is moved down. The work done depends on its weight and how it is moved vertically

Question 18

Work and gpe

Answer 18

Change in objects potential energy store (joules) = weight(newtons) x change of height (meters)

Question 19

Gpe equation

Answer 19

Change of gpe store (joules)= mass(kilograms) x gravitational field strength (newtons/kilogram) x change of height (meters)

Question 20

Gravitational field strength on the moon

Answer 20

Is less than on the earth

Question 21

Kinetic energy

Answer 21

The energy in the kinetic energy store of a moving object depends on its mass and speed

Question 22

Kinetic energy equation

Answer 22

Kinetic energy (joules) = 1/2 mass(kilograms) x speed 2(meters per second)
Ek =1/2 m x v2

Question 23

Elastic potential energy

Answer 23

Energy stored in an elastic object when work is done on the object

Question 24

Elastic potential energy equation

Answer 24

Ee = 1/2 ke2
Elastic potential energy (joules)= 1/2x spring constant(newton per meter) xextension2
E is the extension of the spring

Question 26

What is useful energy?

Answer 26

Energy in the place we want it and in the form we need it

Question 27

What is wasted energy?

Answer 27

Energy that is not useful and is transferred by an undesired pathway. Wasted energy is transferred to the surrounding which becomes warmer. It dissipates and gets less and less useful

Question 28

Efficiency equation

Answer 28

Efficiency =useful output energy transferred by a device(j)/ total input energy supplied to the device (j)

Question 29

What is input energy equal to

Answer 29

Input energy = useful output energy+ energy wasted

Question 30

How can something become more efficient?

Answer 30

Reducing energy wasted by lubricating reducing friction between moving parts

Question 31

How to improve efficiency?

Answer 31

Friction causes heating -lubricate moving parts to reduce friction Resistance of wire causes wire to get hot when current passes through it-use wires with little electrical resistance as possible Air resistance causes a force on a moving object that opposes its motion- streamline the shape of the moving object to reduce this Sound created by machinery causes energy to transfer to the surroundings- cut out noise (tighten lose part to reduce vibrating)

Question 32

How efficient can something be?

Answer 32

No energy transfer can be more than 100% efficient you can never get more energy from a machine than you put in it

Question 33

Comparing energy used in electrical appliances

Answer 33

Light bulb-light emitted from glowing filament-energy transferred from filament heating Electrical heater-energy heating the surroundings- light emitted from the glowing element Electrical toaster-energy heating bread-heats the toaster case and air around it Electrical kettle-energy heating water- energy heating the kettle itself Hairdryer-kinetic energy of air driven round the fan- sound of fan motor and energy heating the hairdryer Electrical motor- kinetic energy of objects driven by the motor. Gravitational potential energy of objects lifted by the motor- energy heating the motor and energy transferred by sound waves generated by the motor

Question 34

What is power?

Answer 34

The rate of energy transfer. The more powerful an appliance is the faster the rate at which it transfers energy.

Question 35

Power equation

Answer 35

Power(watts)=energy transferred to appliance (joules)/time taken for energy to be transferred (seconds) P=E/t

Question 36

Efficiency and power equation

Answer 36

Efficiency =useful power/total power x100

Question 37

Wasted power equation

Answer 37

Power wasted= total power in -useful power out