1.4 Energy concepts
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1
What is work used to calculate?
Effect of forces acting on a body in terms of energy
2
What is the equation for work?
W = F x
3
What is the equation for work-done at an angle?
W = Fxcos(0)
4
What does the conservation of energy state?
Energy can be transferred between multiple forms but is never created nor destroyed
5
How many types of energy are there? What are they?
3
Gravitational potential energy (GPE)
Elastic potential energy (EPE)
Kinetic energy (KE)
Gravitational potential energy (GPE)
Elastic potential energy (EPE)
Kinetic energy (KE)
6
What is the equation for GPE?
ΔEp = mgΔh
(m=mass, g=gfs, Δh= change in height of body)
(m=mass, g=gfs, Δh= change in height of body)
7
What is the equation for EPE?
Ep = 1/2kx^2
(k=spring constant, x=spring extension)
(k=spring constant, x=spring extension)
8
What is the equation for KE?
Ek = 1/2mv^2
(m=mass, v=speed)
(m=mass, v=speed)
9
What will a body falling toward earth lose? What will it gain?
Lose gravitational potential energy (gpe)
Transferred to kinetic energy as speeds up
Transferred to kinetic energy as speeds up
10
What happens when a spring is released, what does it lose?
Lose elastic potential energy
11
What does the work energy relationship relate?
Relates the work done by constant force on body to kinetic energy of body
12
What is the work energy relationship equation?
Fx = 1/2mv^2 - 1/2mu^2
13
What does the work energy relationship equation demonstrate?
That the work done on a body = the change in kinetic energy of that body
14
What is power?
Rate of transfer of energy /
Power is the rate of doing work (if include work)
Power is the rate of doing work (if include work)
15
What is the equation for power?
Power = energy transferred/work done
—————————————-
time
—————————————-
time
16
What are dissipative forces?
Forces that reduce the efficiency of a system
17
What do dissipative forces reduce?
Useful energy, eg. kinetic
18
What do dissipative forces produce?
Un-useful energy, eg. heat
19
What are examples of dissipative forces?
Drag
Friction
Friction
20
Example of friction being a dissipative force?
Friction on car tyre, reduces KE produced by engine
Heats up the tyres reducing performance
Heats up the tyres reducing performance
21
Example of drag being a dissipative force?
Drag on aeroplane, larger energy output required from engine to maintain speed
22
How are vehicles adapted to reduce drag and friction?
Sports cars have pointier front so air can flow over easier
23
What do athletes (cyclists) do to reduce air resistance acting on them?
Wear tight clothing and special headgear
24
What is the equation for energy efficiency?
Efficiency = useful energy transfer
————————————————- x 100
total energy input
————————————————- x 100
total energy input
25
What is the theoretical efficiency of a system?
The max theortical efficiency of system is 100% bc u cant transfer more energy than u put in (conservation of energy)
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