Chapter 8- Energy- forces doing work Flashcards
What happens to energy in a closed system
There is no net change to the total energy in that system
Explain how the energy of a system can be changed, eg- Through work done by forces
Force to move it- energy transferred to gravitational potential force
Explain how the energy of a system can be changed, eg In electrical equipment
Electric lamp transfers electrical energy into light energy
A car engine converts chemical energy into kinetic energy
Explain how the energy of a system can be changed, eg In heating
Kettle- electrical energy input is converted into kinetic energy which in turn changes to heat energy.
What is energy transferred equal to (joules)
Work done (joules) When an object is moved by a force, energy is transferred and work is done. Bu work is not a form of energy- it is one of the ways in which energy can be transferred
Whats the work done formula triangle
E
F D
What is the gravitational potential energy calculation
GPE- m x g x h
take g to be 10
What is the kinetic energy equation
KE- 0.5 x m x v2
When energy dissipates what happens? give examples.
The energy is transferred to its surroundings and is stored in less useful ways. Eg- an electric lamp with 100J of energy, 10 J is used as light and 90 J is used as heat.
When do mechanical processes become wasteful?
When they cause a rise in temperature so dissipating energy in heating the surroundings
Define power
The rate at which energy is transferred, a 100W light bulb will transfer more electrical energy each second than a 60W light bulb would.
What is power measured in
Watts
What is the formula triangle for power
E
P t
What is one watt equal to
one joule per second J/s
What is the equation for efficiency?
useful energy transferred by the device / total energy supplied to the device
