Unit 1.4 - Energy Concepts Flashcards
1
Q
Work definition
A
The transfer of energy as an object moves (it displaces it)
2
Q
The transfer of energy as an object moves
A
Work
3
Q
Work done formula
A
Fx = cos(O)
4
Q
Fx = cos(O)
A
Work done
5
Q
Work unit
A
J
6
Q
Which is the only component that contributes to work?
A
The x component
7
Q
What is f in the work done formula?
A
Force applied
8
Q
What is x in the work done formula?
A
Displacement
9
Q
What is cos(O) in the work done formula?
A
The angle between f and x
10
Q
What changes when work is done?
A
Kinetic enegry
11
Q
When does kinetic energy change?
A
When work is done
12
Q
What is the change in kinetic energy if work is done against the motion of an object?
A
Negative change in kinetic energy
13
Q
What is the change in kinetic energy if work is done with the motion of an object?
A
Positive change in kinetic energy
14
Q
If there’s a negative change in kinetic energy, describe the work done
A
Against the motion of an object
15
Q
If there’s a positive change in kinetic energy, describe the work done
A
Work done with the motion
16
Q
Energy definition
A
The ability to do work
17
Q
The ability to do work
A
Energy
18
Q
Energy unit
A
J
19
Q
Which two concepts in physics have cylindrical definitions?
A
Work and energy
20
Q
Are work and energy scalar of vector? Why?
A
Scalar, as they have no direction
21
Q
Do work and energy have direction? Why?
A
No, as they’re scalar measurements
22
Q
As work and energy have no direction, what can they be instead?
A
(+) or (-)
23
Q
Kinetic energy
A
Energy of motion
24
Q
Energy of motion
A
Kinetic energy
25
Energy of location
Potential energy
26
Potential energy
Energy of location
27
Kinetic energy formula
1/2 mv^2
28
1/2mv^2 formula
Kinetic energy
29
What is m in the kinetic energy formula?
Mass (kg)
30
What is v in the kinetic energy formula?
Velocity
31
What is the work energy theorem (worded)?
Net work = final KE - initial KE
32
Work energy theorem equation
Fx = 1/2mv^2 - 1/2mu^2
33
What is Fx = 1/2mv^2 - 1/2mu^2?
Work energy theorem
34
If the net work is negative, what does this mean?
Work done BY the system
35
Negative net work
Work done BY the system
36
If the net work it positive, what does this mean?
Work done ON the system
37
Positive net work
Work done ON the system
38
Potential energy formula
E = mgΔh
39
E = mgΔh
Potential energy
40
If an object is higher, how does its potential energy change?
More potential energy
41
What changes for an object when it’s higher up?
Its potential energy, which is higher
42
When is ALL of the potential energy converted into kinetic energy when an object travels down something (e.g - a ramp)?
With zero resistive forces
43
With zero resistive forces when an object travels down something (e.g - a ramp), what happens to the energy?
All of the potential energy is converted into kinetic energy
44
What does the fact that, with zero resistive forces, all of the potential energy is transferred into kinetic energy allow us to do?
The velocity at the end of the ramp
45
Under which conditions can we calculate the velocity at the end of a ramp?
When there’s no resistive forces so all of the potential energy is transferred into kinetic energy
46
Give 2 examples of resistive forces
Friction and air resistance
47
What are friction and air resistance examples of?
Resistive forces
48
What do resistive forces cause in terms of energy conversation?
Causes some of the initial potential energy to be converted to thermal energy
49
Under which conditions is potential energy converted into thermal energy when an object moves down something (e.g - a ramp)?
With resistive forces
50
What is thermal energy?
The label for the work done against the resistive forces
51
What is the label for the work done against the resistive forces?
Thermal energy
52
Describe the final velocity of an object when resistive forces act?
Lower
53
Under which conditions is the final velocity of an object lower?
With resistive forces
54
How can we calculate the work done against resistive forces?
Difference between initial PE and final KE
55
What does the difference between intial PE and final KE calculate?
The work done against resistive forces
56
How do we calculate the mean resistive force acting on a body?
1. Calculate the initial potential energy
2. Calculate the final kinetic energy
3. Calculate the work done against the resistive force (the difference between these two)
4. Mean force = work/displacement (W=fx rearranged)
57
Mean force
Work done
——————
Displacement
(W = fx rearranged)
58
Elastic potential energy definition
The energy stored in a material under tension (or compression)
59
The energy stored in a material under tension (or compression)
Elastic potential energy
60
What does elastic potential energy apply to?
Any elastic material (often a spring)
61
What type of energy occurs to elastic materials?
Elastic potential energy
62
Elastic potential energy equation
E=1/2kx^2
63
E=1/2kx^2
Elastic potential energy
64
What’s ‘k’ in the elastic potential energy equation?
Spring constant (Nm-1)
65
Spring constant unit
Nm-1
66
What’s ‘x’ in the elastic potential energy equation?
Change in length (extension)
67
Spring constant
‘k’ in the elastic potential energy formula
The amount the material increases in length per unit force
68
The amount a material increases in length per unit force
Spring constant (Nm-1)
69
Alternative equation for elastic potential energy
W = 1/2fx
70
F=kx
Hooke’s law
71
What is elastic potential energy stored in a spring equal to?
Work done
72
What’s the gradient on a force-extension graph for a spring?
k (spring constant) (Nm-1)
73
How do you calculate the energy in a spring using a force-extension graph?
Force x distance in this direction
=area under the graph
W = 1/2fx
74
W = 1/2fx
Energy in a spring (work done) - alternative equation
(Only use it on spring questions!)
75
Work done = elastic potential energy stored in the spring
…Provided what?
Provided that Inelastic deformation hasn’t occurred
76
If Inelastic deformation occurred, which rule would not be accurate anymore with springs?
That work done = elastic potential energy stored in the spring
77
Power
The rate of energy transfer
78
The rate of energy transfer
Power
79
Describe power
The amount of energy that is transferred per second
80
What is the amount of energy that is transferred per second known as?
Power
81
Unit of power
W
82
W is the unit of…
Power
83
What IS 1 W?
1Js-1
84
1Js-1
1W
85
Equation for power
P = W/t = ΔE/t
86
P = W/t = ΔE/t
Equation for power
87
What do we do for ΔE in the power equation?
Input necessary energy equation
88
What is W in the power equation?
Work done
89
What is ΔE in the power equation?
Change in energy (J)
90
What would a high rate of transferring energy give us?
High power
91
What would give us a high power?
A high rate of transferring energy
92
What would a low rate of transferring energy give us?
A low power
93
What would give us a low power?
A low rate of transferring energy
94
What do resistive forces such as air resistance and friction cause energy to be lost as?
Cause energy to be lost as internal energy in the atoms in the objects and surroundings
95
When is energy lost as internal energy and in what?
Resistive forces (e.g - friction, air resistance), in the atoms in the objects and surroundings
96
Efficiency equation
Useful energy transfer
——————————— x100%
Total energy input
97
What causes energy to be transferred from a system and reduce the overall efficiency of the system?
Dissipating forces (e.g - friction or drag)
98
Draw an energy transfer diagram from potential to kinetic energy
(Check notes)
99
What’s 1 Watt in Joules?
1W = 1Js-1
100
How can an absolute uncertainty be calculated?
Range
———
2
101
What is work done?
Force in the DIRECTION of travel
102
Which height do we use for gravitational potential energy?
Directly upwards - if we’re given an angled slope, we must calculate the change in height directly upwards from it
103
What happens in terms of work when kinetic energy is transferred into gravitational potential energy?
Work is done against gravity
104
When is work done against gravity?
When kinetic energy is transferred into gravitational potential energy
105
What must we always refer to when transferring between types of energy?
Work done
106
When is work done?
During the transfer of energy
107
How is kinetic energy lost to air resistance?
Object hits air molecules
Looses kinetic energy
Gains heat energy
108
How is heat energy gained?
When an object loses kinetic energy when hitting air molecules (air resistance)
109
Describe the force in the work done equation
Force in DIRECTION OF TRAVEL
110
Spring constant gradient
Nm^-1
111
Work done definition
Force x distance in direction of force
112
Elastic potential energy in a slack rope
0J
113
Spring constant
Tension per unit extension
