energy and matter Y9

what is the formula for kinetic energy in symbols?

KE = ½ mv²

what is the formula for kinetic energy in words?

kinetic energy = 0.5 x mass of object x speed²

what is efficiency?

a measure of how much of the total input energy is transferred to useful output energy

what is the formula for efficiency that involves energy?

efficiency = useful energy OUT/ total energy IN

what is the formula for efficiency that involves power?

efficiency = useful power OUT/ total power IN

what is the unit for efficiency?

there is no unit

how is efficiency expressed?

as a decimal or a percentage

what is one of the causes of inefficiency in a moving machine?

friction

what is one way to increase the efficiency of a moving machine?

use lubricant to decrease friction

what is power?

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

what are the two formulae for power in words?

P = E/t

P = W/t

what are the two formulae for power in words?

Power = Energy transferred/ time

Power = Work done/ time

what is the unit for power?

Watts (W)

what is a watt?

a joule per second (J/s)

what is the useful energy transfer of a falling object?

GPE to KE

what is the wasted energy transfer of a falling object?

GPE to thermal

what is the energy transfer for an object being projected upwards?

KE to GPE

what is the energy transfer for something falling in a gravitational field?

GPE to KE

what is the energy transfer for a vehicle slowing down?

KE to thermal

how is energy transferred when a moving object hits an obstacle?

transferred by waves (sound) to the kinetic store of the particles in the object, obstacle and surroundings

AND

transferred by heating to the thermal store of the object, obstacle and surroundings

how is energy transferred when an object is moving due to force?

transferred mechanically to the kinetic store of the object

how is energy transferred from the mains supply to the water in a kettle?

transferred by electricity to the thermal store of the heating element, then transferred by heating to the thermal store of the water

why does gas have lower density than a solid?

its particles are spread out, taking up a larger volume

how can you measure the volume of a cube (or cuboid)?

multiply length by width by height

what do you use to measure the mass of an object?

a balance

what is internal energy?

total of the kinetic energy and potential energy of all the atoms in an object

what happens to a material if the kinetic energy of the atoms change?

temperature changes

what happens to a material if the potential energy of the particles change?

it changes state

what is specific heat capacity?

the amount of energy required to raise the temperature of one kilogram of a substance by one degree

if you heat a solid, what happens to its temperature as it is melting?

while it is melting the temperature stays the same

what is specific latent heat of fusion?

the energy required to melt one kilogram of a substance

if you heat a liquid, what happens to its temperature as it is boiling?

while it is boiling the temperature stays the same

what is specific latent heat of vaporisation?

energy required to change one kilogram of a substance from liquid to vapour

if you plot a graph of temperature of a substance against time and the line is flat, what is happening?

it is changing state

what will happen to a hot drink left on a table in a kitchen?

it will cool down until it reaches the temperature of the room