P1 - Energy Flashcards
State the 8 energy stores
- Thermal
- Kinetic
- Gravitational potential
- Elastic potential
- Chemical
- Magnetic
- Electrostatic
- Nuclear
Description of Magnetic energy store
Is the energy stored when repelling poles have been pushed closer together or when attracting poles have been pulled further apart.
Description of thermal energy store
In hotter objects, the particles have more internal energy and vibrate faster
Description of Chemical energy store
The energy stored in chemical bonds, such as those between molecules
Description of kinetic energy store
The energy of a moving object
Description of electrostatic energy store
The energy stored when repelling charges have been moved closer together or when attracting charges have been pulled further apart
Description of elastic potential energy store
The energy stored when an object is stretched or squashed
Description of gravitational potential energy
The energy of an object at height.
Examples of magnetic energy store (3)
- Fridge magnets
- compasses
- maglev trains which use magnetic levitation
Examples of thermal energy store
- Human bodies
- hot coffees
- stoves or hobs
- Ice particles vibrate slower, but still have energy
Examples of chemical energy store
- Foods
- muscles
- electrical cells.
Examples of kinetic energy stores
- Runners
- buses
- comets
Examples of electrostatic energy store
- Thunderclouds,
* Van De Graaff generators
Examples of elastic potential energy store
- Drawn catapults
- compressed springs
- inflated balloons
Examples of gravitational potential energy
- Aeroplanes
- kites
- mugs on a table
State the 4 energy transfers
- mechanically (by a force doing work)
- electrically (work done by moving charges)
- heating
- radiation (e,g light or sound)
What happens when a system changes
- Energy is transferred
- It can be transferred into or away from the system
- Or between different objects in the system or between different types of energy stores
What happens in a graph when energy in given out (exothermic) (and draw it)
Downwards around as energy is released
What happens in a graph when energy is taken in (endothermic)
An upwards arrow which shows that energy is taken in
Conservation of energy principle
Energy can be transferred usefully, stored or dissipated but can never be created or destroyed
Example of the conversation of energy principle (3)
- A mobile phone is a system
- When the phone is used, energy is transferred usefully from chemical energy store (battery)
- But some energy is dissipated to thermal energy store of phone
- Phone starts to become hot as it is used for a while
Dissipated energy
No longer useful when it heats the environment
Describe energy transfers for closed systems (4)
- A cold spoon is dropped into an insulated flask of hot soup then sealed
- The flask is a perfect thermal insulator so spoon and soup form closed system
- Energy transferred from the energy store of soup to the useless thermal energy store of spoon
- Energy transfers have occurred within the system, but no energy has left the system - net change is zero
What happens when energy is transferred between stores
- Not all of the energy is transferred usefully into the store that you want it to go
- Some energy is always dissipated when an energy transfer takes place
Energy transfers in a pendulum
- Gains gravitational potential energy due to increased height
- When released this energy becomes transferred to kinetic energy
Energy transfers in a bungee
- When the person starts to fall freely, it speeds up as it falls
- The energy transferred from gravitational potential to kinetic energy store
What is a closed system
Is a system in which no energy transfers take place out of or into the energy stores of the system
What is energy measured in?
Joules (J)
Describe the action of frictional forces on objects and the associated heating effect (3)
- Friction works against the motion and acts in the opposite direction
- When one object is sliding on another it starts to slow down due to friction
- By rubbing them together we generate friction and therefore heat
Why do objects become heated by frictional forces
When friction acts some useful kinetic energy is transferred to dissipated heat energy
The formula to work out work done
Work done (J) = Force (N) x Distance (m)
State the factors which affect the change in the gravitational potential energy store of a system
- The higher an object is lifted the more energy that is transferred to the store
- The amount of the store depends on mass height and strength of the gravitational field the object is in
The effect of gravitational field strength on gravitational potential energy
- The stronger the gravitational field strength the more gravitational potential energy
- The less gravitational field strength the more gravitational potential energy
Equation for gpe
Mass (Kg)x gravitational field strength (N/kg) x height (m)
Equation for kinetic energy
Kinetic energy (j)= 0.5 x mass (kg) x (speed)2 (m/s)
Equation for elastic potential (j)
0.5 x spring constant (N/m) x (extension)2 (m)
Equation for change in thermal energy (j)
Mass (kg) x specific heat capacity (J/kg°C) x temperature (°C)
The specific heat capacity of a substance
Is the amount of energy required to raise the temperature of one kilogram of the substance by one celsius degree
Specific heat capacity required practical (7)
1) To investigate a solid material (e,g copper) you’ll need a block of the material with two holes in it (for heater and thermometer to go inside)
2) measure the mass then warp in an insulating layer (e,g newspaper) to reduce the energy transferred from the block to the surroundings - the. Insert heater and thermometer
3) measure initial temp - set potential difference of power supply to 10V - turn on the power supply and start a stop watch
4) temp of material may increase - electrical to thermal energy store in power supply
5) take readings of the temp every minute for 10 minutes - should find that current does not change as the block heats up
6) then turn off supply - using P=VI calculate the power supplied to the heater - use this to calculate energy transferred to the heater using (E=Pt)
7) Plot a graph of energy transferred to the thermal energy store of the block against temperature
Power
- Is the rate at which energy is transferred
* Or, the rate of doing work
Equations for power (2)
- Power (w)= energy transferred (j) divided by time(s)
* Power (w) = work done (j) divided by time(s)
Example of power (4)
- It take 8000J of work to lift a stunt performer to the top of a building
- Motor A can lift the stunt performer to correct height in 50 secs
- Motor B would take 300secs to lift the performer to the same height
- Both motors transfer the same amount of energy but motor A would do it quicker than motor B so motor A is the more powerful motor
Ways of reducing unwanted energy transfers (2)
- Lubricants - can reduce the friction between objects’ surfaces when they move e,g oil
- Thermal insulation e,g Cavity walls, loft insulation, double glazed windows, Draught excluders
What happens when the thermal conductivity of a material increase
The rate of the energy transfer by conduction across the material increases
How is the rate of cooling of a building affected by the thickness and thermal conductivity
The thicker the walls and the lower the thermal conductivity, the slower the rate of energy transfer will be - the building will cool more slowly
Equation for efficiency (2)
- Useful output energy transfer divide by total input energy transfer
- Useful power output divided by total power input
Ways to increase efficiency of an intended energy transfer (4)
- waste less energy
- insulating objects
- Lubricating them
- making them more streamlined
