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Arnav's GCSE Physics > Topic 5 - Forces > Flashcards

Topic 5 - Forces Flashcards

1
Q

What is a scalar quantity?

A

a quantity that only has a magnitude
A quantity that isn’t direction dependent

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2
Q

What is a vector quantity?

A

A quantity that has both a magnitude and an associated direction.

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3
Q

How can a vector quality be drawn and what does it show?

A

As an arrow
The length of the arrow represents the magnitude
The arrow points in the associated direction

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4
Q

What is a force?

A

A push or pull acting on an object due to an interaction with another object.

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5
Q

What two categories can all forces be split into?

A

Contact and non-contact

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6
Q

Examples of contact forces

A

Friction, Air Resistance, Tension

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7
Q

Examples of non-contact forces

A

Gravitational, Electrostatic, magnetic

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8
Q

Is force a vector or scalar quantity?

A

Vector: has both magnitude and direction

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9
Q

Three examples of vectors

A

Velocity, displacement, force

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10
Q

Three examples of scalar quantities

A

Temperature, time, mass, speed, distance, energy

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11
Q

Weight

A

The force that acts on an object due to gravity and the object’s mass.

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12
Q

What quantities does weight depend on?

A

W = mg
Mass and gravitational field strength

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13
Q

Unit for weight?

A

Newton (N)

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14
Q

Unit for gravitational field strength?

A

N/kg

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15
Q

Centre of mass

A

The single point where an object’s weight can be considered to act through.

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16
Q

How do you measure weight?

A

Newton-meter or calibrated spring balance.

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17
Q

Resultant force

A

Single force equivalent to all other forces acting on a given object.

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18
Q

What does a force doing work mean?

A

The force causes an object to be displaced through a distance.

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19
Q

Work done equation

A

Work done = fd (force x distance)
units are joules, newtons and metres

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20
Q

What distance must be used when calculating work done?

A

Distance that is moved along the line of action of the force.

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21
Q

When is 1 joule of work done?

A

When a force of 1 Newton causes a displacement of 1 m.

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22
Q

Newton-metres to Joules conversion

A

1:1 (it’s the same)

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23
Q

What occurs when work is done against frictional forces?

A

A rise in temp of the object
Kinetic energy is converted to heat

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24
Q

Why does air resistance slow down a projectile?

A

The object does work against air resistance
Kinetic energy is converted to heat, slowing the object down

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25
Relationship between force applied and extension of an elastic object
Extension is directly proportional to force applied, provided that the limit of proportionality is not exceeded.
26
What is an inelastic deformation?
A deformation that results in the object being permanently stretched The object doesn't return to it's original shape when the force is removed
27
Force, spring constant and extension equation w units
Force = spring constant x extension (F= ke) units are Newtons, Newton-metres and metres
28
What type of energy is stored in a spring when stretched?
Elastic potential energy
29
What can extension be replaced with in equation for spring force?
Compression
30
Moment
the turning effect of a force
31
Moment equation
Moment = Force * distance units are Nm, newtons and metres
32
What distance measurement is used when calculating a moment?
Perpendicular distance from the pivot to the line of action of the force.
33
If an object is in equilibrium, what can be said about the moments acting on the object?
The clockwise moments are equal to the anticlockwise moments.
34
What makes up a lever system?
Load Effort Pivot
35
How is a lever used as a force multiplier?
If the distance between the effort and pivot is greater than the distance between the pivot and load, the force applied on the load is greater than the effort force. This is since the moment on both the effort and load must be the same.
36
Give an example of when a lever may be used to multiply a force.
A wrench, which has a long handle so that the force applied by the user is multiplied
37
What determines the moment of a gear?
the size of the wheel
38
Describe the moment and speed of a larger gear being driven by a smaller gear.
Larger wheel will rotate more slowly but produces a larger moment
39
What is a fluid?
A liquid or a gas
40
What angle do the forces due to pressure act on a given surface in any fluid?
Right angles to the surface
41
Equation for pressure
Pressure = Force/Area Units are Pascals, Newtons and m^2
42
What happens to the density of the atmosphere as you get higher?
The atmosphere becomes less dense as altitude increases.
43
Explain why atmospheric pressure decrease with an increase in heght.
Pressure is created by collisions of air molecules The quantity of molecules decreases as the height increases This means atmospheric pressure decreases with an increase of height
44
Atmosphere
Layer of gas surrounding the Earth
45
How does pressure in fluids increase with depth?
As the depth increases, the mass of liquid above that depth also increases. This means that the force due to the mass increases. Since the force has increased whilst the area has remained constant, the pressure will increase.
46
Why does pressure in fluids increase with density?
As the density increases, the number of particles in a given volume increases. Consequently, the weight of the fluid is greater. This means that the force from the fluid above a certain point is larger. Since the force has increased, the pressure also increases.
47
Equation for pressure in liquids
P = pgh Units are pascals, kg/m^3, N/kg and m
48
Why are objects in a fluid subject to an upthrust?
When an object is submerged in a fluid, it has a higher pressure below it than it does above, as there is more weight at the bottom than there is at the top. This leads to an upward force called upthrust. You float or sink depending on whether the upthrust is more or less than your weight.
49
What is upthrust always equal to?
The weight of the fluid that the object displaces.
50
What factors influence whether an object will sink or float?
Upthrust Weight Density of fluid
51
Why will an object denser then water never be able to float?
If the density is too high, there would not be enough volume displaced to produce an upthrust larger than the object's weight, which means that it will sink.
52
Speed of sound
330 m/s
53
Human Walking Speed
1.5 m/s
54
Human Running Speed
3 m/s
55
Human Cycling Speed
6 m/s
56
speed equation
speed = distance/time
57
Why can an object travelling at a constant speed in a circle not have a constant velocity?
Speed is scalar Velocity is vector which means it can only be constant if the direction is constant In circular motion the direction is continuously changing
58
Speed from a distance-time graph
Gradient of the graph
59
Speed from distance time graph where object is accelerating
Draw a tangent to the curve and calculate a gradient
60
Acceleration equation
Change in Velocity / Time Taken units are m/s^2, m/s, s
61
Distance from a velocity-time graph
Area under the graph
62
Acceleration of free fall
9.8 m/s^2
63
Resultant force at terminal velocity
0 - terminal velocity is a constant speed so isn't accelerating
64
Newton's First Law for stationary object
If resultant force is 0, object will remain at rest
65
Newton's First Law for moving object
If resultant force is 0, object will remain at constant velocity
66
braking forces and driving forces at constant velocity
Braking forces are equal to the driving forces
67
If an object changes direction but remains at a constant speed, is there a resultant force
Yes - if there is a change in direction, there is a change in velocity and therefore there must be a resultant force.
68
Inertia
Tendency of an object to continue in it's state of rest or uniform motion
69
Newton's Second Law
F = ma
70
Newton's Second Law in Words
An object's acceleration is directly proportional to the resultant force acting on it and inversely proportional to it's mass.
71
Inertial mass
How difficult it is to change a given object's velocity The ratio of Force over Acceleration
72
Newton's Third Law
Whenever two objects interact, the forces that they exert on each other are always equal and opposite.
73
Stopping distance
Sum of thinking distance and driving distance
74
For a given braking distance, if vehicles speed is increased what can be said about it's stopping distance?
Stopping distance is increased with an increase in speed
75
Range of values for human reaction time
0.2-0.9
76
Factors affecting a driver's reaction time
Tiredness Drugs Alcohol
77
Factors affecting braking distance
Wet/Icy roads Poor brake conditions Poor tire conditions
78
Energy Transfers when a car brakes.
Work is done by friction between brakes and wheel Kinetic energy converted to heat and is dissipated to the surroundings through the brake discs
79
To stop a car in a certain distance, if it's velocity is increased what must happen to the braking force applied?
Must also be increased
80
Consequences of large decelerations
Brakes could overheat Could lose control of the vehicle
81
Momentum equation
mass x velocity
82
Momentum unit
kg m/s (kilogram metres per seconds)
83
Momentum in a closed system
Total momentum before is equal to the total momentum afterwards
84
Momentum, force and time equation
Force * Time = Change in Momentum
85
What is equal to the force in a collision?
Rate of change of momentum
86
If change in momentum is fixed, what is the only way to reduce force that the object experiences?
Increase length of time over which the change of momentum occurs.
87
How does a seatbelt improve a passenger's safety during a collision?
Passenger must decelerate from the vehicle's velocity at impact to 0, meaning they undergo a fixed change of momentum The force they experience is equal to the rate of change of momentum Seatbelts increase the time over which the force is applied, reducing force experienced

Arnav's GCSE Physics (8 decks)

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