Unit 1.4 - Energy Concepts Flashcards
Work definition
The transfer of energy as an object moves (it displaces it)
The transfer of energy as an object moves
Work
Work done formula
Fx = cos(O)
Fx = cos(O)
Work done
Work unit
J
Which is the only component that contributes to work?
The x component
What is f in the work done formula?
Force applied
What is x in the work done formula?
Displacement
What is cos(O) in the work done formula?
The angle between f and x
What changes when work is done?
Kinetic enegry
When does kinetic energy change?
When work is done
What is the change in kinetic energy if work is done against the motion of an object?
Negative change in kinetic energy
What is the change in kinetic energy if work is done with the motion of an object?
Positive change in kinetic energy
If there’s a negative change in kinetic energy, describe the work done
Against the motion of an object
If there’s a positive change in kinetic energy, describe the work done
Work done with the motion
Energy definition
The ability to do work
The ability to do work
Energy
Energy unit
J
Which two concepts in physics have cylindrical definitions?
Work and energy
Are work and energy scalar of vector? Why?
Scalar, as they have no direction
Do work and energy have direction? Why?
No, as they’re scalar measurements
As work and energy have no direction, what can they be instead?
(+) or (-)
Kinetic energy
Energy of motion
Energy of motion
Kinetic energy
Energy of location
Potential energy
Potential energy
Energy of location
Kinetic energy formula
1/2 mv^2
1/2mv^2 formula
Kinetic energy
What is m in the kinetic energy formula?
Mass (kg)
What is v in the kinetic energy formula?
Velocity
What is the work energy theorem (worded)?
Net work = final KE - initial KE
Work energy theorem equation
Fx = 1/2mv^2 - 1/2mu^2
What is Fx = 1/2mv^2 - 1/2mu^2?
Work energy theorem
If the net work is negative, what does this mean?
Work done BY the system
Negative net work
Work done BY the system
If the net work it positive, what does this mean?
Work done ON the system
Positive net work
Work done ON the system
Potential energy formula
E = mgΔh
E = mgΔh
Potential energy
If an object is higher, how does its potential energy change?
More potential energy
What changes for an object when it’s higher up?
Its potential energy, which is higher
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
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
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
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
Give 2 examples of resistive forces
Friction and air resistance
What are friction and air resistance examples of?
Resistive forces
What do resistive forces cause in terms of energy conversation?
Causes some of the initial potential energy to be converted to thermal energy
Under which conditions is potential energy converted into thermal energy when an object moves down something (e.g - a ramp)?
With resistive forces
What is thermal energy?
The label for the work done against the resistive forces
What is the label for the work done against the resistive forces?
Thermal energy
Describe the final velocity of an object when resistive forces act?
Lower
Under which conditions is the final velocity of an object lower?
With resistive forces
How can we calculate the work done against resistive forces?
Difference between initial PE and final KE
What does the difference between intial PE and final KE calculate?
The work done against resistive forces
How do we calculate the mean resistive force acting on a body?
- Calculate the initial potential energy
- Calculate the final kinetic energy
- Calculate the work done against the resistive force (the difference between these two)
- Mean force = work/displacement (W=fx rearranged)
Mean force
Work done
——————
Displacement
(W = fx rearranged)
Elastic potential energy definition
The energy stored in a material under tension (or compression)
The energy stored in a material under tension (or compression)
Elastic potential energy
What does elastic potential energy apply to?
Any elastic material (often a spring)
What type of energy occurs to elastic materials?
Elastic potential energy
Elastic potential energy equation
E=1/2kx^2
E=1/2kx^2
Elastic potential energy
What’s ‘k’ in the elastic potential energy equation?
Spring constant (Nm-1)
Spring constant unit
Nm-1
What’s ‘x’ in the elastic potential energy equation?
Change in length (extension)
Spring constant
‘k’ in the elastic potential energy formula
The amount the material increases in length per unit force
The amount a material increases in length per unit force
Spring constant (Nm-1)
Alternative equation for elastic potential energy
W = 1/2fx
F=kx
Hooke’s law
What is elastic potential energy stored in a spring equal to?
Work done
What’s the gradient on a force-extension graph for a spring?
k (spring constant) (Nm-1)
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
W = 1/2fx
Energy in a spring (work done) - alternative equation
(Only use it on spring questions!)
Work done = elastic potential energy stored in the spring
…Provided what?
Provided that Inelastic deformation hasn’t occurred
If Inelastic deformation occurred, which rule would not be accurate anymore with springs?
That work done = elastic potential energy stored in the spring
Power
The rate of energy transfer
The rate of energy transfer
Power
Describe power
The amount of energy that is transferred per second
What is the amount of energy that is transferred per second known as?
Power
Unit of power
W
W is the unit of…
Power
What IS 1 W?
1Js-1
1Js-1
1W
Equation for power
P = W/t = ΔE/t
P = W/t = ΔE/t
Equation for power
What do we do for ΔE in the power equation?
Input necessary energy equation
What is W in the power equation?
Work done
What is ΔE in the power equation?
Change in energy (J)
What would a high rate of transferring energy give us?
High power
What would give us a high power?
A high rate of transferring energy
What would a low rate of transferring energy give us?
A low power
What would give us a low power?
A low rate of transferring energy
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
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
Efficiency equation
Useful energy transfer
——————————— x100%
Total energy input
What causes energy to be transferred from a system and reduce the overall efficiency of the system?
Dissipating forces (e.g - friction or drag)
Draw an energy transfer diagram from potential to kinetic energy
(Check notes)
What’s 1 Watt in Joules?
1W = 1Js-1
How can an absolute uncertainty be calculated?
Range
———
2
What is work done?
Force in the DIRECTION of travel
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
What happens in terms of work when kinetic energy is transferred into gravitational potential energy?
Work is done against gravity
When is work done against gravity?
When kinetic energy is transferred into gravitational potential energy
What must we always refer to when transferring between types of energy?
Work done
When is work done?
During the transfer of energy
How is kinetic energy lost to air resistance?
Object hits air molecules
Looses kinetic energy
Gains heat energy
How is heat energy gained?
When an object loses kinetic energy when hitting air molecules (air resistance)
Describe the force in the work done equation
Force in DIRECTION OF TRAVEL
Spring constant gradient
Nm^-1
Work done definition
Force x distance in direction of force
Elastic potential energy in a slack rope
0J
Spring constant
Tension per unit extension
