P1 Flashcards
How can energy be transferred?
Heating
Waves
Electric current
Or when a force moves an object
What energy transfers happen when a roaler coaster moves down?
GPE transferred to
Kinetic
Thermal (air resistance and friction)
Some energy transferred by Sound waves
How does a pendulum work?
As the bob on a pendulum moves away from the middle the kinetic store decreases and the GPE increases.
If air resistance is small then the bob will reach the same height on each side
What would happen if you put a pendulum in a vacuum? Why? What would this be an example of?
It would swing forever
As there is no air resistance (no energy transferred and no net change to the energy stored in the system)
A closed system
What is a system?
Is an object or a group of objects.
What is the conservation of energy?
Energy can’t be created or destroyed
Where is energy transferred in a bungee jump?
GPE
Kinetic
Elastic potential
Jumper comes to a stop
What is the energy transferred of someone going back up from a bungee jump?
Elastic Potential dec
Kinetic inc
GPE inc
Why doesn’t the bungee jumper return to original height?
Some energy was transferred to the thermal energy store of the surroundings by heating as the rope stretched and then shortened again.
What does it mean when the rope is slack?
Not tight
No tension
What must you do to raise an object?
You need to use a force that will overcome the force of gravity on it.
Energy transferred=
Work done on it
The work done by a force depends on the — of the force and the — moved
Size
Distance
What is the equation for work done?
Force applied (F) (Newtons) x Distance moved (s) (metres)
What is the unit of work done?
Joules
When an object moved down, the energy in its GPE store decreases
This — is — to the work done by the gravitational force acting on it
Decrease
Equal
What does the work done when an object moves up or down depend on?
Weight of object
Distance moved vertically (change of height)
What is it equation for change in objects gravitational potential energy store (J)
Weight (Newtons) x Change of height (Metres)
What is equation for change in GPE store?
Mass (kg) x gravitational field strength (Newtons/kg) x change of height (metres)
What is kinetic energy?
The energy an object has because of its motion
This depends on its mass and speed
What is the equation for kinetic energy?
1/2 x mass (kg) x speed ^2 (metres/ second)
What is hooke’s law?
The graph
F = ke
What happens when you run on a running machine?
As you exercise energy is transferred to the thermal energy store of your muscles (making u hot) and to the thermal energy store of the machine by the force you exert to overcome the friction in the machine.
Input energy =
Useful output energy
As energy can’t be created or destroyed
What is the equation for efficiency?
Useful output energy transferred by device (J)
——————————————————-
Total input energy supplied to the device (J)
The more powerful an appliance is…
The faster the rate at which it transfers energy.
What is the power of an appliance measured in?
Watts or Kilowatts
How many watts in a kilowatt?
1000
How many joules of energy are transferred with 1 watt?
1 watt is equal to the rate of transferring 1 joule of energy in 1 second
1 kw is equal to 1000 joules per second or 1kj/s
What is the calculation for power?
Energy transferred to appliance (joules)
——————————————————-
Time take for energy to be transferred (s)
The useful output power is the useful energy transfers per — transferred by it.
Second
What is the second equation for power?
Useful power out
———————— x 100
Total power in
What is the equation for power wasted?
Total power in - total power out
