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MED 101- PHYSICS I > 5. ENERGY > Flashcards

5. ENERGY Flashcards

1
Q
  1. What is energy?
A
  • energy is the ability to do work or to heat object
  • it can be converted from one form to another
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2
Q
  1. Can you name a few forms of energy?
A
  • electrical energy
  • mechanical energy
  • chemical energy
  • gravitational energy
  • radiant energy
  • nuclear energy
  • magnetic energy
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3
Q
  1. 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
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4
Q
  1. 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

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5
Q
  1. 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
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6
Q
  1. 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
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7
Q
  1. 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
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8
Q
  1. 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
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9
Q
  1. 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)
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10
Q
  1. 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
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11
Q
  1. How would the equation to find the work of an object be written?
A

W= F// x d

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12
Q
  1. What is another equation by which the work on a object can be found?
A

W= F x d x cosθ

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13
Q
  1. 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
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13
Q
  1. 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

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14
Q
  1. 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
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15
Q
  1. 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
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16
Q
  1. 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
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17
Q
  1. 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
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18
Q
  1. What is the unit of work done by a constant force on an object?
A
  • Nm
  • Newtons x metres
  • IT IS CALLED A JOULE
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19
Q
  1. 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
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20
Q
  1. 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
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21
Q
  1. When is an object said to have energy?
A
  • when the object is in motion
  • and it has the ability to do work
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22
Q
  1. What is Kinetic Energy?
A
  • it is the energy an object has due to its motion
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23
Q
  1. What are some examples of Kinetic Energy?
A
  • meteors
  • walking
  • falling
  • throwing a ball
  • a flying airplane
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24
Q
  1. What is the equation of Kinetic Energy?
A
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25
Q
  1. 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
  1. What is the full unit of Kinetic Energy?
A
  • kg.㎡/s²
27
Q
  1. Is kinetic energy a scalar or a vector quantity?
28
Q
  1. 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
  1. What do different types of forces bring about?
A
  • different types of potential energies
30
Q
  1. 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
  1. 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
  1. 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
  1. What is the formula to work out Gravitational Potential Energy?
A

PEgravitational= mg x h

34
Q
  1. 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
  1. 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
  1. 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?
37
Q
  1. 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
  1. What is another name for a Non-Conservative force?
A
  • a dissipative force
39
Q
  1. 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
  1. Name the three conservative forces?
A
  • Gravitational Force
  • Elastic Force
  • Electric Force
41
Q
  1. Name the four non- conservative forces?
A
  • Friction
  • Air Resistance
  • Tension in the cord
  • Push or pull forces exerted by a person
42
Q
  1. Can potential energy be applied to Non-Conservative forces?
A
  • no
  • it can only be defined for conservative forces
43
Q
  1. 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
  1. What is the equation for Mechanical Energy?
A

Emechanical= KE + PE
= Kinetic Energy = Potential Energy

45
Q
  1. 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
  1. 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
  1. 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
  1. 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
  1. What happens to the temperature of two surfaces when they slide against each other?
A
  • it is increased
50
Q
  1. What does the work done by friction equal to?
A
  • the lost mechanical energy
51
Q
  1. 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
  1. 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
  1. What is the definition of power?
A
  • the rate at which work is done
  • the rate at which energy is transferred

54
Q
  1. 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
  1. 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
  1. What is the SI unit for Power?
A
  • joules per second
  • J/s
  • this is known as a WATT
57
Q
  1. What is another equation that shows how power can be worked out?
A

P= F x v
= Force x Velocity

58
Q
  1. What powers the human body?
A
  • Metabolism
59
Q
  1. 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
  1. 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
  1. Read through summary one.
    Do you understand everything?
62
Q
  1. Read through summary two.
    Do you understand everything?

MED 101- PHYSICS I (28 decks)

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