5. ENERGY Flashcards
1
Q
- What is energy?
A
- energy is the ability to do work or to heat object
- it can be converted from one form to another
2
Q
- Can you name a few forms of energy?
A
- electrical energy
- mechanical energy
- chemical energy
- gravitational energy
- radiant energy
- nuclear energy
- magnetic energy
3
Q
- What is the work done on an object?
A
- it is the process by which energy is transferred from one form to another
- it describes how much energy is transferred from one form to another
- it informs us what kind of process was involved in order to transfer this energy
4
Q
- Provide a definition for the work done on an object?
A
- the product of the displacement and the component of the force parallel to the displacement
5
Q
- What kind of energy does an object gain and lose when it is falling?
WHY
A
- it gains kinetic energy
- it loses potential energy
- this is because the gravitational field of the Earth is working on the object to accelerate it
6
Q
- In the absence of other forces such as air resistance, what is the amount of work done on an object?
A
- it is the numerical increase in the kinetic energy of the object
7
Q
- Let’s say you are pushing an object up a hill.
What kind of force is currently acting on the object?
A
- a constant force
8
Q
- What two factors are taken into consideration when working out the work done on an object?
A
- the force with which the object is acted upon
- the distance covered by the object
9
Q
- What would increase the work done on the object when it is being pushed up the hill?
A
- the hill would be longer (more distance)
- the hill would be stepper (more force)
10
Q
- How is the work done on an object by a constant force defined as?
CONSTANT: constant magnitude and constant direction
A
- the magnitude of the displacement x the component of the force parallel to the displacement
11
Q
- How would the equation to find the work of an object be written?
A
W= F// x d
12
Q
- What is another equation by which the work on a object can be found?
A
W= F x d x cosθ
13
Q
- Is the work done on an object a vector or a scalar quantity?
A
- it is a scalar quantity
- it has a magnitude
- this magnitude can be positive or negative
- it does not have a direction
13
Q
- What are each of the components in this equation:
W= F x d x cosθ
A
W= the work done on an object
F= the magnitude of the constant force acting on the object
d= the magnitude of the displacement of the object
θ= the angle between the direction of the force and the direction of the displacement
14
Q
- When is this equation: W= F x d x cosθ, used?
A
- when the force which produces the displacement is not parallel or acting in the same direction as the constant force
15
Q
- When the Force and the displacement act in the same direction, what is the outcome?
A
- θ= 0°
- the magnitude of the Work is greater than zero
- the magnitude is positive
16
Q
- When the Force and the displacement act in the opposite direction, what is the outcome?
A
- θ= 180°
- the magnitude of the work is less than zero
(this is due to the presence of a friction force) - the magnitude is negative
17
Q
- When the Force and the displacement act in the perpendicular direction to each other, what is the outcome?
A
- θ= 90°
- the magnitude of the work done is zero
- this is because there is no such vector component
18
Q
- What is the unit of work done by a constant force on an object?
A
- Nm
- Newtons x metres
- IT IS CALLED A JOULE
19
Q
- What are two examples when a force does no work?
A
- when the force acts on an object and does not move it
- when the force acts perpendicular to the motion/the constant velocity
- this can happen when an object is carried at a constant velocity by a force which acts on the object at 90° to the direction of the motion
20
Q
- What is important to specify when we deal with work?
A
- whether the work is done by a specific object
- or whether it is done on a specific object
- whether work done is due to one particular force acting on the object
(specify which source it is) - whether the total/net work done is due to the total/net force acting on the object
21
Q
- When is an object said to have energy?
A
- when the object is in motion
- and it has the ability to do work
22
Q
- What is Kinetic Energy?
A
- it is the energy an object has due to its motion
23
Q
- What are some examples of Kinetic Energy?
A
- meteors
- walking
- falling
- throwing a ball
- a flying airplane
24
Q
- What is the equation of Kinetic Energy?
A
25
Q
- Is there a direct connection between work and kinetic energy?
If so, why is this significant?
A
- yes there is
- this means that Kinetic energy is also measured in joules
26
Q
- What is the full unit of Kinetic Energy?
A
- kg.㎡/s²
27
Q
- Is kinetic energy a scalar or a vector quantity?
A
- scalar
28
Q
- What is Gravitational Potential Energy/Potential Energy?
A
- the energy an object possesses due to its position relative to a reference point
- it is the energy associated with forces that depend on the position/configuration of an object/objects relative to their surroundings
29
Q
- What do different types of forces bring about?
A
- different types of potential energies
30
Q
- Why does a heavy brick being held high above the ground have potential energy?
A
- because of it’s position relative to the earth
- the raised brick has the ability to do work
- it will fall to the ground due to the gravitational potential energy acting on it
- while it falls to the ground, it will experience kinetic energy acting on it
31
Q
- What is needed for an object of mass (m) to be lifted vertically?
A
- an upward force must be exerted on the object
- this force needs to be at least equal to the weight of the object (mg)
32
Q
- What is necessary to lift the object of mass (m) without acceleration?
A
-an external force must be exerted on the object
- this external force is equal to the weight of the object (mg)
33
Q
- What is the formula to work out Gravitational Potential Energy?
A
PEgravitational= mg x h
34
Q
- What happens if the object has no vertical height (vertical position y) relative to its reference point?
A
- then there is no Gravitational Potential Energy acting on the object
- the gravitational potential energy is not dependent on the horizontal position of the object
35
Q
- What is the work done by gravitational force dependent on?
A
- it only depends on the initial and the final positions of the object
- it does not depend in the path taken by the object
- THEREFORE:
PEgravitational= mg x (final position-initial position)
36
Q
- What is the value of the work done by gravity if we move an object of mass around and then back to it’s starting point?
A
- ZERO
37
Q
- What is a conservative force?
A
- a force in which the work done by a force does not depend on the path taken
- any choice of paths taken by the object will still result in the same amount of work done
38
Q
- What is another name for a Non-Conservative force?
A
- a dissipative force
39
Q
- What is a dissipative force?
A
- dissipative forces are forces of such nature that energy is lost from a system when motion takes place
- the work done depends on the path taken
40
Q
- Name the three conservative forces?
A
- Gravitational Force
- Elastic Force
- Electric Force
41
Q
- Name the four non- conservative forces?
A
- Friction
- Air Resistance
- Tension in the cord
- Push or pull forces exerted by a person
42
Q
- Can potential energy be applied to Non-Conservative forces?
A
- no
- it can only be defined for conservative forces
43
Q
- What is the Total Mechanical Energy of a system?
A
- it is the sum of the kinetic and the gravitational potential energies at any moment
44
Q
- What is the equation for Mechanical Energy?
A
Emechanical= KE + PE
= Kinetic Energy = Potential Energy
45
Q
- What effect does a non-conservative/dissipative force have on the mechanical energy of the system?
A
- it removes the mechanical energy from the system under consideration
46
Q
- What effect do conservative forces have on the amount of mechanical energy in the system?
A
- they do not change the amount of mechanical energy in the system
47
Q
- What is the Principle of the Conservation of Energy?
A
- the total amount of energy in a closed system does not increase or decrease
- a closed system is one which does not exchange energy with it’s surrounding
- in the absence of air resistance or any external forces, the mechanical energy of an object is constant
48
Q
- What is the Law of Conservation of Energy?
A
- The total energy in a system cannot be created nor destroyed; only transformed from one form to another
49
Q
- What happens to the temperature of two surfaces when they slide against each other?
A
- it is increased
50
Q
- What does the work done by friction equal to?
A
- the lost mechanical energy
51
Q
- What does the lost mechanical energy transformed into?
How could we write this in the form of a formula?
A
- thermal energy
- this thermal energy could be measured with a sensitive thermometer
52
Q
- What is the change (▵E thermal) Thermal energy related to?
How would we write this in the form of a formula?
A
- it is related to the magnitude of the frictional force
- AND the magnitude of the displacement
- CAUSED by the external force
53
Q
- What is the definition of power?
A
- the rate at which work is done
- the rate at which energy is transferred
54
Q
- What is power equal to?
How would we write this in the form of an equation?
A
- it is equal to the work done divided by the time taken to do it
55
Q
- What is the power rating of an engine referring to?
A
- how much chemical or electrical energy can be transformed into mechanical energy
per unit time
56
Q
- What is the SI unit for Power?
A
- joules per second
- J/s
- this is known as a WATT
57
Q
- What is another equation that shows how power can be worked out?
A
P= F x v
= Force x Velocity
58
Q
- What powers the human body?
A
- Metabolism
59
Q
- Is all energy always utilised by the machine that it is put in?
A
- no
- it can be wasted by the machine
- some of it may be lost to dissipative (non-conservative) forces
- this can be noticed as heat or sound
- this is why the energy input is not the same as the output (as work done)
60
Q
- What is the Mechanical Efficiency/Efficiency of a system?
How would we write is as a formula?
A
- the ratio of output power to input power
61
Q
- Read through summary one.
Do you understand everything?
A
- yes
62
Q
- Read through summary two.
Do you understand everything?
A
- yes
