P1- Energy

Question 1

Is energy ever used up?

Answer 1

NO! It’s transferred between different energy stores and objects

Question 2

What are the eight energy stores of an object?

Answer 2

1) Thermal energy stores/Internal energy stores
2)Kinetic energy stores
3)Gravitational potential energy stores
4)Elastic potential energy stores
5)Chemical energy stores
6)Magnetic energy stores
7)Electrostatic energy stores
8)Nuclear energy stores

Question 3

What are the ways that energy can be transferred?

Answer 3

-Mechanically (by a force doing work)
-Electrically (work done by moving charges)
-By heating (changes thermal energy store of object)
-By radiation (e.g. light or sound)

Question 4

A system=

Answer 4

A single object (air in a piston) or a group of objects (two colliding vehicles) that you’re interested in

Question 5

What happens when a system changes?

Answer 5

Energy is transferred (can be transferred into or away from system, between different objects in system or between different types of energy stores)

Question 6

What’s a closed system?

Answer 6

System where neither energy nor matter can enter or leave. There is no net change in total energy.

Question 7

Work done is another way of saying…

Answer 7

energy transferred

Question 8

How can work be done?

Answer 8

When current flows (work is done against resistance in circuit) or by a force moving an object

Question 9

Give two examples of work being done:

Answer 9

The INITIAL FORCE exerted by a person to throw a ball upwards does work. It causes an energy transfer from the chemical energy store of the person’s arm to the kinetic energy store of the ball and arm.

Question 10

The energy in a kinetic energy store depends on what two factors of an object?

Answer 10

It’s mass and speed.
The greater the mass and the faster it goes=more kinetic energy

Question 11

What is the unit for Kinetic energy (Ek)?

Answer 11

Joules, J
The equation for kinetic energy is:
Ek=1/2 x m x v^2
(J) (kg) (m/s)

Question 12

What does the amount of energy in a gravitational potential energy store of an object depend on?

Answer 12

The object’s mass, object’s height (how high it is), and the strength of the gravitational field the object is in.

Question 13

What is the unit of Gravitational potential energy (Ep)?

Answer 13

Joules, J
Ep= m x g x h
(J) (kg) (N/kg) (m)

Question 14

For a falling object when there’s no air resistance:
Energy lost from the g.p.e store=

Answer 14

Energy gained in the kinetic energy store

Question 15

Does air resistance act against all falling objects?

Answer 15

Yes- causes some energy to be transferred to other energy stores (e.g. thermal energy stores of object and surroundings)

Question 16

How is energy transferred to an elastic potential energy store?

Answer 16

By stretching or squashing an object

Question 17

What equation is used for elastic potential energy (Ee)?

Answer 17

Ee= 1/2 x k x e^2
(J) (N/m) (m)
k=spring constant
e=extension

Question 18

Define Specific heat capacity

Answer 18

The amount of energy needed to raise the temp of 1kg of a substance by 1 degrees celsius.

Question 19

Give the equation that links energy transferred to specific heat capacity

Answer 19

Change in thermal energy(J) = mass(kg) x specific heat capacity(J/kg°C) x change in temperature (°C)

Question 20

What is the conservation of energy principle?

Answer 20

Energy can be TRANSFERRED usefully, stored or dissipated (wasted, not lost but just not used usefully- eg. thermal energy in a phone), but can NEVER be CREATED or DESTROYED.

Question 21

What type of energy stores are batteries in phones?

Answer 21

Chemical energy stores

Question 22

What about energy transfers in a closed system?

Answer 22

Energy can be transferred in a closed system and some can be dissipated in that closed system but that energy never leaves the system. For example, a spoon in a hot flask of soup that has a lid on it (assuming it’s a perfect insulator)- energy in the thermal energy store of the soup is transferred to the useless thermal energy store of the spoon which cools down the soup slightly. Energy transfers have occurred within the system but no energy has left the system- so net energy change=zero.

Question 23

What is power?

Answer 23

Rate of energy transfer/rate of doing work

Question 24

What is power measured in and what does that unit mean?

Answer 24

Watts, W
One watt= 1 joule of energy transferred per second

Question 25

Power can be calculated using either…

Answer 25

P(W)=E(J)/t(s)
P(W)=W(J)/t(s)
Energy and work done are the same thing just depends on the question.

Question 26

What is the definition of a powerful machine?

Answer 26

One that transfers a lot of energy in a short space of time.
(e.g. two identical cars race, the car with the more powerful engine will reach the end faster than the other car- i.e. it will transfer the same amount of energy but over less time)

Question 27

What state does conduction occur mainly in?

Answer 27

Solids

Question 28

What is conduction?

Answer 28

The process when VIBRATING PARTICLES TRANSFER ENERGY to NEIGHBOURING PARTICLES.

The particles can vibrate as the energy transferred to the object via heating is stored in the object’s thermal energy store and then that energy is shared across the kinetic energy stores of the particles in the object.

Question 29

What is thermal conductivity?

Answer 29

A measure of how quickly energy is transferred through a material via conduction (the particles vibrating and transferring energy between particles’ kinetic energy stores, this continues until the energy is transferred to the other side of the object).

Question 30

What usually happens when the energy has been fully transferred to the other side of the object through the vibrating particles?

Answer 30

It’s usually transferred to the thermal energy store of the surroundings (or anything touching the object).

Question 31

What state does convection occur only in?

Answer 31

Liquids and gases

Question 32

What is convection?

Answer 32

Where energetic particles MOVE AWAY from HOTTER to COOLER REGIONS.

Question 33

How does the density of a heated region of a liquid or gas decrease?

Answer 33

-Energy transferred to system’s thermal store via heating
-Energy is shared across kinetic energy stores of system’s particles
-Unlike in solids, particles in liquid and gas can move
-When region is heated, particles move faster and space between individual particles increases
-Causing density of heated region to decrease (less mass in a certain volume)

Question 34

Why will the WARMER and LESS DENSE region rise above the DENSER and COOLER regions in a liquid/gas?

Answer 34

Liquids and gases can flow.
Cooler Denser region will be below WARMER and LESS DENSE region.
Think of water, more dense than water then it is below water.
Warmer air rises above COOLER air.

Question 35

If there is a constant heat source, what can be created?

Answer 35

A convection current. This is basically a continuous cycle of convection.

Question 36

What type of heating device relies on creating convection currents in the air of the room in order to heat the room?

Answer 36

A radiator.
Page 15 on Physics Guide is the process