Energy - energy

What is kinetic energy?

Kinetic energy is the energy stored in moving objects

What is the equation for kinetic energy?

E_k=0.5 x m(Kg) x v²(

Kinetic image(J) = 0.5 x m(Kg) x v²⁽M/s)

What is elastic potential energy?

When a spring is stretched, a force is applied to change the length of the spring and it the spring extends

The stretched spring is storing this energy and this is the elastic potential energy

How is the extension plotted on a graph?

The extension is directly proportional to the force so staight line is drawn on the graph

However if too much force is applied, the spring has reached the limit of how far it can extend which is called the limit of proportionality

When the limit of proportionality is met, what are the affects on the spring?

It can no longer return to its original length if the force is taken away

What is the equation for elastic potential energy?

E_e= 0.5 x K x e²

Elastic potential energy(J) = 0.5 x spring constant(N/m) x e²(m)

What is applying a force called?

Doing work

What is gravitational energy?

The energy stored in an object due to its position above the earths surface which is due to the force of gravity acting on an object

What is the equation for gravitational potential energy?

E_p = m x g x h

Gravitational potential energy(J) x mass(Kg) x gravitational field strength (N/kg) x height (m)

Measures the force of gravity

What are the units for mass?

Kilograms

What are the units for height?

Meters

What is thermal energy?

The energy stored due to a objects temperature

What is specific heat capacity?

The specific heat capacity of a substance is the amount of energy required to raise the temperature of 1 kg substance by 1’c

What is the equation to calculate the specific heat capacity?

△E = m x c x △θ

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

What is the law of conservation of energy?

Energy can be transfered usefully, stored or dissipated but it cannon be created or destroyed

What is a pendulum?

A mass attached to a string attached to a fix point

This set up is called a system

What is a system?

A system is an object or a group of objects

What is a closed and opened system?

In a closed system, no energy can enter or leave

In a opened system, energy can enter or leave

How does energy transfer in pendulum?

What is a problem with the pendulum?

It does not consider friction

Friction causes energy to be transfered to thermal energy which are less useful which means the energy have been dissipated (wasted)

It is wasted as the energy is not used for its intended purpose

This causes the pendulum to gradually swing with less energy and eventually stop

How do we reduce unwanted energy transfers?

Unwanted energy transfers can be reduced by reducing friction

How can we reduce friction in the pendulum?

• Use a lubricant on the fixed point

• Remove the air particles from around the pendulum

What are the energy transfers in bungee jumping?

• Standing on the platflorm

• As the jumper falls

• When the rope starts to tighten

• When its fully extended

• The bungee jumper starts by standing on a platform and all the energy stored in the system is gravitational potential energy

• As the jumper falls, energy is transferred from the gravitational potential energy store to the kinetic energy store

• When the bungee rope starts to tighten, the kinetic energy store is now at its maximum

• When the rope is fully extended, the kinetic energy is at 0 as the jumper is not moving and all the energy has transferred to the elastic potential energy store

• The rope recoils and energy is transferred from the elastic potential energy back to the kinetic energy stor e

• During the ascent up, energy transfers from the kinetic energy store back to the gravitational potential energy store

• At the top, all the energy is gravitational potential energy

What is the key idea of the bungee jump?

The jumper never returns back to the original position

This is because energy is dissipated as thermal energy

This is due to:

• Friction with air particles

• Stretching effects in the bungee rope which is not fully elastic (some thermal energy is dissipated)

What happens when a car brakes?

The brake presses against the wheel causing friction

This means the kinetic energys store of the car is transferred to thermal energy store in the breaks

This means the temperature of the breaks increases and the car slows done and stops

What does ‘work done’ mean?

Work done is whenever energy is transferred from one store to another

What is mechanical work?

Using a force to move an object

What is electrical work?

Energy transferred in a current

What is the equation for work done?

Work done(J) = force (N) x distance (m)

This tells us the energy transfer between to stores

What is power?

The rate at whuch energy is transferred or the rate at which work is done

Measured in watts

What are the two equations for power?

Power(W) = energy transferred(J) / time(S)

Power(W)= work done(J) / time (S)

What is power in watts directly proportional to?

1 watt is an energy transfer of 1 J per second

What does efficiency tell us?

Efficiency tells us what fraction of the energy we put into a appliance is transferred to useful forms of energy

What are the two equations for efficiency?

Efficiency = useful output energy transfer / total input energy transfer

Efficiency = useful power output / total power input

These must be calculated in this exact order or you will get a value greater then 1 or 100%

How do we calculate a decimal to a percentage to get the percentage of efficiency?

Times by 100

How can we increase the efficiency of a energy transfer?

• Use a pan with a wider base and lid

• Place the heating element inside the water

What does conductivity mean?

How efficient a material is at keeping thermal energy/heat in

High conductivity = allow a lot of thermal energy out

Low conductivity = reduces the amount thermal energy passing through

How are houses kept warm?

Houses have a internal breezeblock wall and a external brick wall that have a gap inbetween called a cavity

The cavity if filled with insulating material which has a low thermal conductivity which helps keep heat in

Houses also have loft insulation

How are windows designed to keep heat in?

Windows are double glazed to have a low thermal conductivity

Required pratical 1: specific heat capacity

• Place a beaker onto a balance and press zero

• Now add oil to the beaker and record the mass of the oil from the balance

• Place a thermometer and an immersion heater into the oil

• Read the starting temperature of the oil

• Add insulating foam to reduce thermal energy transfer to the surroundings

• Connect a joulemeter to the immersion heater (this tells us the how many jewls of electrical energy passes through the immersion heater)

• Leave for thirty minutes

• Read the total number of joules of energy that passed into the immersion heater and the final temperature of the oil

What to do with the specific heat capacity required pratical results?

Change in thermal energy = mass x specific heat capacity x temperature change

Rearrange this equation for find the specific heat capacity

Specific heat capacity = change in thermal energy / mass x temperature change

Why may result of the specific heat capacity required pratical be inaccurate?

• Thermal energy passing out of the beaker into the air

  • Use an insulator with a lower thermal conductivity

• Not all thermal energy passing into the oil

  • Ensure that immersion heater is fully submerged

• Incorrectly reading of the thermometer

  • Use on electronic temperature probe

• Thermal energy may not be spread through the oil

  • Stir the oil

What are examples of use of energy in the modern world?

• Transport

• Generating electricity

• Heating

What are the three main fossil fuels?

• Coal

• Oil

• Gas

What are the advantages to fossil fuels?

• Reliable

• Fossil fuels release a great deal of energy

• Abundant

• Cheap

• Verstile (can use for many things)

• Portable

What are the disadvantages of fossil fuels?

• Release large amounts of carbon dioxide

• Non-rewnable (not being replaced as we use them and will one day run out)

• Can release of pollutants eg sulfur dioxide

What are the features of nuclear power?

• Non-rewnewable

• Run on uranium and plutonium

What are the advantages of nuclear power?

• Does not contribute to climate change

• Reliable

What are the disadvantages of nuclear power?

• Highly dangerous radioactive material

• Decommissioning (take down) a nuclear power plant takes many years

• Extremely expensive

• Produces large of amounts of highly dangerous radioactive waste

What big changes ocurd that made the use of coal fall?

• The use of nuclear power increased

• The uk began to become a producer of oil and gas which started to replace coal

What were the advantages to switching from coal to gas?

• Burning gas produces less carbon dioxide

• Gas-fired power stations are flexible and can be switched on quickly in demand

What are the disadvantages of renewable resources?

• Expensive

• Unreliable

How do we fix the problem of renewable resources being unreliable?

• Baseloads can be used which is a constant supply of electricity thats on all the time

• Gas-fired power stations can be used to provide emergency power

What is renewable energy?

A renewable energy resource is one that is being or can be replenished as it is used

What are the advantages of all renewable energy resources?

• Renewable

• Do not add carbon dioxide to the atmosphere

What is wind power? What is the disadvantage of wind power?

Wind power harnesses the kinetic energy of moving air to generate electricity

• Unreliable

What is solar power? What is the disadvantage of solar power?

Solar power converts energy from the sun into power

• Unreliable

What is hydroelectric power? What are the advantages and disadvantages of hydroelectric power?

Hydroelectric power uses the energy of moving water to generate electricity

• Reliable

But

• Requires rivers

• Causes damage to habitats

What is the advantage of tidal power?

• Reliable

What is geothermal energy? What are the advantages?

Geothermal energy uses heat from the earth to generate electricity and heat buildings

• Reliable

What is a problem with renewable resources only generating electricity?

A lot of energy used in the Uk is for cars which run of petrol or diesel which are fossil fuels

What is biofuels? What are the advantages and disadvantages ?

Biofuels are produced from plant materials

• Burning biofuels does not add extra carbon dioxide to the atmosphere

• Can be used to power vehicles

But

• Using land to grow crops for fuel could push up the price of food as less land is being used to grow it