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Motion, Forces & Energy Flashcards

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1
Q

Describe Energy efficiency

A

Percentage of useful energy transferred

No energy in the real world is 100% efficient

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2
Q

What is the formula for (energy) efficiency?

A

Efficiency (%) = (Useful energy/Total energy) x 100

Applicable to energy transfers and power

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3
Q

What is a Sankey Diagram?

What does a Sankey Diagram show?

A

A diagram showing transfers of energy while also showing how much energy is transfered to different places.

Looks like an arrow that splits into other arrows

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4
Q

Would a light bulb produce more, equal or less energy than the initial input?

A

Less
Because no energy transfer is 100% efficient, some energy has to be lost on the way

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5
Q

Def. pressure

A

A measure of force per Area

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6
Q

What is the formula for pressure?

A

P = F/A
P = Pressure (Pa)
F = Force (N)
A = Area (m2)

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7
Q

What does SI stand for?

A

System internationale

The accepted system to use for physics

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8
Q

What is the unit uses for N/m2

A

Pascals (Pa)

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9
Q

What is 100 cm2 converted to metres?

A

0.01m2

Divide by 1002

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10
Q

Why will a small object and a large object experience the same pressure at the bottom of lake?

A

Because pressure is per volume already, so the formula takes that into account.

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11
Q

What is the formula for pressure in liquids

A

P = ρgΔh
P = Pressure (Pa)
p = Density (kg/m^3)
g = Gravitational field strength (9.8m/s2)
Δh = Change in depth (m)

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12
Q

What is the formula for moments

A

τ = Fd

τ = moments (nm)
F = Force (N)
d = distance (m) (from pivot)

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13
Q

How do you find center of mass if object is irregular

A

Object must be hung at different points and a vertical line directly drawn.
The intersection of those lines shows center of gravity.

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14
Q

How do you find the center of mass in a regular object

A

Find geometrical center

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15
Q

Define center of mass/ gravity

A

The point where gravity or weight appears to act through

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16
Q

What do we know about momentum?

A

Always conserved
Vector

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17
Q

What is the formula for momentum

A

p = mv

p = momentum (kg m/s)
m = mass (kg)
v =velocity (m/s)

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18
Q

Define momentum

A

this def is a bit wonky, …

The amount of ‘oumph’ an object has, or better :
The amount of force required to stop the movement of an object

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19
Q

What are elastic collisions

A

Kinetic energy and momentum conserved

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20
Q

What are inelastic collisions

A

Kinetic energy and momentum not conserved,
due to energy loss in other forms
e.g. heat and sound

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21
Q

What equation can we create using
p = mv
To solve a problem with two moving objects that stick together, based on the fact that momentum is conserved (elastic momentum)

A

before collision (A, B) After collision (AB)

pA + pB = pAB

mA vA + mB vB = m AB v AB

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22
Q

Explain momentum conservation

A

If momentum is conserved, means
total momentum before collision = total momentum after collision

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23
Q

Def: mass

A

Kg - amount of matter that makes up an object

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24
Q

Def. Weight

A

N - force on an object due to a gravitational field

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25
Q

What is the formula for Fg ?
Give names and units

A

mass (kg)
I
Fg = mg — Acceleration due to gravity (m/s^2)
I
Force due to gravity (N)
(also weight)

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26
Q

A seesaw has a pivot which is too much in the left. In the middle of the seesaw, there is a force acting. what is it?

A

? is the weight of beam, pivot point

The beam itself will create a turning effect because pivot is not on pivot point

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27
Q

What are 2 other ways to say ‘moment’?

A

Torque
Turning effect

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28
Q

EASER EGG! HAHA!

A

boy, take a break, please!

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29
Q

Equilibrium:
Bob and Rob are standing on a see-saw again. They should know better.

Bob: 80 kg Rob : ? kg
____________________________________________
2.4m <——————-> ∆ <————>1.3 m

A

Fg = mg
Fg = 80 x 9.8
Fg = 1881.6

Fg = T/d
F = 1447.38 N

+ m = fg/g
m = 147.69 kg

OMG Rob!! no more chocolates for you!!

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30
Q

What is an equilibrium

A

When the turning effect on both sides of the pivot is equal

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31
Q

Def. Moments

A

A turning effect on an object around a pivot point

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32
Q

What is the weight force if the mass is 20kg?

A

see for yourself :

20 x 9.8 = 196 N

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33
Q

How do you find total distance traveled?

Speed

A
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34
Q

How do you find total distance traveled?

Speed

A

Vxt

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35
Q

How do you find the total distance travelled in a speed-time graph?

A

s = v x t

Find the area of shapes then ad together to get the total area

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36
Q

What happens to velocity in circular motion

A

Constantly changing,
always accelerating,
this means it needs force to keep spinning

a = ∆ v
______
∆ t

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37
Q

Explain why objects in circular motion are always accelerating,
and the direction of the velocity

A

As an object travels at constant speed, and it moves around a path, the direction is constantly changing.
As velocity is a vector quantity, a change in direction of an object means its velocity is also changing .
Due to the formula, a = ∆v/∆t, acceleration is also constantly changing.
The direction of velocity is perpendicular to the centripetal force.

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38
Q

rearrange the acceleration formula to find the change in time

A

∆t = ∆v/a

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39
Q

In circular motion, when is a stronger force needed for a constant acceleration?

A
  • larger mass (with constant v and r)
  • smaller radius ( with constant m and v)
40
Q

What is 3km/h in m/s ?

A

= 3000 m / 3600s
= 0,183 m/s

OR

= 3 divided by 3.6 = 0,83 m/s

41
Q

What is friction
Which state of matter provide friction
(other than solids)

A

A force between 2 surfaces, may impede motion and produce heating

Friction (drag) acts on objects moving through liquids, and through gases (e.g. air resistance)

42
Q

What is the formula for Hooke’s Law

A

K = F/ x

K is Spring constant (N/m), the amount of resistance a spring has
F is force (N)
x is extension (n)

43
Q

What is the other formula for K = F/x ?

A

F = (-)Kx

F is force (N)
x is extension (n)
K is Spring constant (N/m)
x is negative if spring is compressed

44
Q

What is the acceleration due to earth due to gravity

A

9.8 m/s^2

45
Q

What is the formula for density (+ units)

A

p = m/v

p is density (g/ml)
m is mass (g)
v is volume (m^3)

46
Q

What are the effect of stacking springs in parallel vs in series

A

In parallel = spring constant x2
In series = spring constant /2

47
Q

What is this

F 𝛼 X

A

Directly proportioned

𝛼 = proportional to

K = F/x

48
Q

With an object moving in circular motion, what are the 2 forces in action ?

A

Velocity and centripetal force

49
Q

Define centripetal force

A

force acting inwards on a circular motion

50
Q

When does the k = fx formula not apply?

A

After the limit of proportionality

51
Q

What is the formula for force concerning circular motion?

A

F = mv^2 / r

F = force (N)
m = mass (Kg)
v = velocity ( m/s)
r = radius (m)

52
Q

How would you find the average speed of the journey?
(graph with distance ad time, speed is not always the same)

A

V = S/t

S = total distance
t = total time

53
Q

How do you find acceleration on a speed -time graph?

A

a = ∆V/ ∆t

∆V = Y axis
∆t = X axis

54
Q

What is Newton’s 2nd law?

A

F = ma

Force = mass x acceleration

The acceleration of an object depends on the mass of object and force applied

55
Q

What is Newton’s 3rd law

A

For each force applied, there is a reaction of an equal and opposite force

56
Q

What is Newton’s first law

A

An object that is stationary will remain that way unless another force acts upon it.
Same with an object that is moving.

57
Q

Explain distance vs displacement

A

Distance is how far an object has travelled, a magnitude, while displacement is how far out of place an object is in a straight line and therefore a vector.

58
Q

How do you find the volume of an irregular object

A

Calculate displacement of water (Eureka!)

59
Q

What is net force ?

A

resultant force
combination of all forces applied

60
Q

What is the difference between

v = s/t and a = ∆V/ ∆t

A

average speed, distance, time

acceleration, change in velocity, change in time

61
Q

1.
————————–>
Km/h m/s
<————————-
2.

A

1.3.6
2.3.6

62
Q

What are the units ?
v,s, t

A

V = Speed (average) (m/s) or
S = Distance (m)
t = time (s)

63
Q

Def. Vector

A

A quantity with a magnitude and a direction

64
Q

Def. Scalar

A

amount

e.g. 250 g

65
Q

a car goes 9km North, 9 km East

How to find angle?
What is displacement
What is distance traveled

A

trigonometry
Distance from start point
Distance travelled

66
Q

Car goes 11 m/s > car goes 4 m/s

What is the change in velocity?

A

V^f -V’ = V change

4 - 11 = -7m/s

67
Q

Easter Egg!!

A

get up and have a little happy dance on the spot !

68
Q

Explain technique how to find question mark:

       b
       ￬ a →    
           ↘︎?
A

Use a pythagorean theorem to find resultant force

69
Q

What is formula for Acceleration

A

a = ∆V / ∆t

∆ = change in
∆ V = change in velocity
∆t = change in time

Direction matters !

0—————> 50 > Velocity = o m/s^2
<—————–

70
Q

What is the unit for Acceleration?

A

m/s^2

71
Q

What is deceleration

A

the opposite of acceleration

  • m/s^2
72
Q

Which equation involves
Average speed Distance and time
How are they represented ?

A

V = s/t

speed is distance dividend by time

you can also represent them in a triangle : S
V t

73
Q

Def. Resultant force

A

10 N 5N
——–> object <———-
￬￬
5N —-> object

74
Q

What is the formula for kinetic energy

A

Ek = 1/2mv^2

Ek = Kinetic energy (J)
m = mass (kg)
v = speed (m/s)

75
Q

What are the main energy transfers

A
  • Mechanical
  • Electrical
  • Heating
  • electromagnetic, sound, other waves …
76
Q

Name 7 sources of energy production

A
  • wind turbines
  • water turbines
  • nuclear
  • fuels
  • geothermal
  • solar
  • tidal / waves
77
Q

Define power

A

The rate at which the work is done/ The rate of energy transfer

78
Q

Def. boiler

A

Uses heat from the burning of fuels to boil water to steam

79
Q

Define Turbine

A

Transforms energy from a fluid (liquid/gas) into rotational kinetic energy

80
Q

Define Generator

A

Consist of a coil (or coils) of wire that rotate in a magnetic field to produce an electric current

81
Q

Define kinetic energy

A

Energy stored in moving objects

82
Q

Describe the energy transfers and stores

  1. torch battery —> 2. —> 3. bulb —> 4. —> 5. Surroundings
  2. bulb —> 6. —> 7. Surroundings
A
  1. Chemical
  2. Electrical
  3. Thermal *
  4. Thermal
  5. Thermal *
  6. Light
  7. Thermal *
  • = Internal
83
Q

How can you find the relationship between the loss of Ep—> the gain of Ek or vice versa

A

Energy is conserved!

Etotal = Ek + Ep

mg ∆ h = 1/2 mv^2

g ∆ h = 1/2 V^2

before after
—————–>

84
Q

How can you find the relationship between the loss of Ep—> the gain of Ek or vice versa

A

Energy is conserved!

Etotal = Ek + Ep

mg ∆ h = 1/2 mv^2

g ∆ h = 1/2 V^2

before after
—————–>
energy is transfered

85
Q

What is the formula for gravitational potential

A

Ep = mg∆h

Ep = gravitational potential (J)
m = mass (kg)
g = gravitational field (9.8 m/s)
∆h = Change in height (m)

86
Q

What are the main energy stores

A

Kinetic
Nuclear
Electrostatic
Thermal
Magnetic
Chemical potential
Elastic potential
Gravitational potential

87
Q

What are the formulae for power

A

p = w/t or p = ∆E / t

p = power (W)
t = time (s)
W = work (J)
∆E = change in energy (J)

88
Q

What is power measured in ?

A

Watts (W)

a.k.a. (J/s)

89
Q

Define “Work”

A

A transfer of energy

“work has been done”

90
Q

What is the formula for work

A

W = Fd

W = Work (J)
F = Force (N)
d = distance (m)

91
Q

What are some hardy rearrangements of

mg∆h = 1/2 mv^2

A

V = √2g∆h

and

∆h = (1/2V^2)/g

92
Q

What is the law of conservation of energy

A

Energy can not be created or destroyed.
I can only be transferred from one store to another.

93
Q

What is the equation for impulse

A

∆p = F∆t

∆p = impulse (Kg m/s)
F = Force (N)
∆t = change in time (s)

94
Q

Define impulse

A

A change of momentum of an object.
It also describes the forces involved during the change in momentum

95
Q

Describe nuclear E
- origin
- advantages/ disadvantages
- transfers

A

EMPTY

96
Q

Describe geothermal E

A

Physics (7 decks)

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