Combined Physics - P1 Energy
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In physics, what is a ‘system’?
A group of objects
What are the four ways in which energy can be transferred?
• Mechanically (by a force doing work) • Electrically (work done by moving charge) • Heating • Radiation (light and sound)
What is work done the same as?
Energy transferred
What equation links kinetic energy, mass and velocity?
Ek = 0.5 x m x v2 Kinetic energy = 0.5 x mass x velocity2
Name the 8 energy stores.
• Thermal • Kinetic • Gravitational Potential • Elastic Potential • Chemical • Magnetic • Electrostatic • Nuclear
What is a closed system?
A system where matter or energy cannot leave or enter.
What equation links gravitational potential energy, mass, gravitational field strength and height?
Ep = m g h Gravitational Potential Energy = mass x gravitational field strength x height
Describe the energy changes involved in a falling ball.
The ball’s gravitational potential energy store decreases. The ball’s kinetic energy store increases.
What are the units for work done?
Joules
What is specific heat capacity?
The amount of energy required to raise the temperature of 1 kg of the substance by 1 oC.
What equation links power, energy transferred and time?
Power = Energy Transferred / Time (P = E/t)
What equation links power, work done and time?
Power = Work done / Time (P = W/t)
Name the energy stored in a stretched or compressed spring.
Elastic potential energy
What does ‘conservation of energy’ mean?
Energy can be transferred, stored or dissipated, but can never be created or destroyed.
Describe the energy transfer involved in a person lifting a weight.
• The person’s chemical energy store decreases. • The kinetic energy store of the person’s arm and the weight increases. • The gravitational potential energy store of the person’s arm and the weight increases.
Describe the energy transfer when work is done by friction.
Kinetic energy store of the object decreases. Thermal energy store of the surroundings increases.
A book on the top shelf has a gravitational potential energy store of 100 J. The book falls. How much energy will be in the book’s kinetic energy store as it hits the ground?
100 J
What is another name for ‘wasted’ energy?
Dissipated energy
What are lubricants used for?
Reduce friction between moving objects.
List some examples of house insulation.
• Cavity wall insulation (reduces convection) • Loft insulation (reduces convection) • Double-glazed windows (reduces conduction) • Draught excluders (reduces convection)
Describe how energy is transferred by convection.
• Particles gain energy • Particles move further apart • The fluid becomes less dense • Particles rise and transfer energy to other particles • The fluid becomes more dense • Particles fall • A convection current is formed
What equation links efficiency, useful power output and total power input?
efficiency = useful power output / total power input
Why are homes insulated?
To reduce heat loss
Describe how energy is transferred by conduction.
• Particles vibrate more • Particles collide with neighbouring particles • Transferring energy