Section 1 - Forces and Their Effects Flashcards
(159 cards)
1
Q
What are vector quantities?
A
Quantities with a size and direction.
2
Q
What are scalar quantities?
A
Quantities with only a size.
3
Q
Give 7 scalar quantities.
A
- Speed
- Time
- Distance
- Temperature
- Mass
- Length
- Energy
4
Q
Give 6 vector quantities.
A
- Velocity
- Force
- Displacement
- Acceleration
- Momentum
- Weight
5
Q
Sort these quantities into vector and scalar: • Speed • Time • Velocity • Distance • Force • Temperature • Mass • Displacement • Acceleration • Momentum • Length • Weight • Energy
A
SCALAR • Speed • Time • Distance • Temperature • Mass • Length • Energy VECTOR • Velocity • Force • Displacement • Acceleration • Momentum • Weight
6
Q
Define velocity.
A
Speed in a given direction.
7
Q
What is the formula for velocity?
A
Velocity = Displacement / Time
8
Q
What do the gradient and area under the line show on a distance-time graph?
A
Gradient: Speed
Area under: Nothing
9
Q
On a distance-time curve, how is the speed calculated?
A
A tangent is drawn, and its gradient is worked out.
10
Q
What is acceleration?
A
The rate at which velocity is changing.
11
Q
How can velocity be changed?
A
- Change in speed
2. Change in direction
12
Q
What is the formula for acceleration?
A
Acceleration = Change in Velocity / Time Taken
13
Q
What is the unit for acceleration?
A
m/s2
14
Q
What is the unit for velocity?
A
m/s
15
Q
What do the gradient and area under the line show on a velocity-time graph?
A
Gradient: Acceleration
Area under: Distance travelled
16
Q
Describe how acceleration, velocity and distance can be found off a velocity-time graph.
A
Acceleration: Gradient
Velocity: Read off y value
Distance: Area under graph
17
Q
What is a force?
A
A push or pull.
18
Q
What are the 6 types of force?
A
1) Gravity/Weight
2) Reaction force (from a surface)
3) Thrust or push or pull (due to engine or rocket)
4) Drag or air resistance or friction
5) Lift (due to an aeroplane wing)
6) Tension (in a rope)
19
Q
What is the resultant force?
A
A single force which has the same effect on an object as all the forces acting on it combined.
20
Q
What force prevents a teapot accelerating downwards when it is placed on a table?
A
The reaction force of the table pushing upwards.
21
Q
What do balanced forces mean in terms of motion?
A
The object is stationary or travelling at a constant speed.
22
Q
What does a resultant force mean in terms of motion?
A
There will be a change in the object’s velocity.
23
Q
How are forces acting in a straight line combined into a resultant force?
A
They are added or subtracted.
24
Q
Remember to revise the parallelogram method!
A
Do it!
25
Who worked out the laws of motion?
Isaac Newton
26
What are the 3 Laws of Motion?
1. If a body is at rest and the forces acting on it are balanced then the body will remain at rest. If the body is moving and the forces acting are balanced then the body will keep moving at constant speed in a straight line.
2. F = ma
3. For every action there is an equal and opposite reaction.
27
If an object is moving, is there necessarily an overall force acting on it?
No, there may be a zero resultant force, which results in constant speed.
28
What is the unit for force?
Newtons
29
What is the equation for force (relative to mass and acceleration)?
F = ma
| Force = Mass x Acceleration
30
What happens, on terms of forces, when you push on a trolley?
The trolley pushes back with an equal and opposite force. Therefore, you accelerate away from each other.
31
What symbol is used for momentum in equations?
p
32
What is momentum?
The tendency of an object to move in a certain direction.
33
What two things affect the momentum of an object?
1. Mass
| 2. Velocity
34
Is momentum vector or scalar?
Vector
35
What is the equation for momentum?
p = m x v
| Momentum = Mass x Velocity
36
What is Conservation of Momentum?
In a closed system, the total momentum before an event (e.g. a collision) is the same after the event.
37
What two things must be worked out when solving a momentum question?
Momentum before the event and momentum after the event.
38
How are a forces and momentum related?
* A force on an object causes a change in momentum.
| * A quick change in momentum causes a large force on the object.
39
How do car safety features work?
* They increase the time over which the change of the passenger's momentum happens (i.e. Increase collision time)
* This decreases the rate of change of momentum and thus reduces the force acting on the passenger, so they are less likely to be injured.
40
What does 'closed system' mean?
There are no external forces acting on the event.
41
What is the equation for force (relative to momentum and time)?
Force = Change in momentum / Time taken
42
What is the unit for momentum?
kg m/s
43
What is the unit for mass?
kg
44
Give some examples of safety features which work by increasing collision time.
* Seat belts
* Air bags
* Cycle helmets
* Cushioned surfaces in playgrounds
* Crash mats in gyms
45
Why will an object always stop is there is no force propelling it along?
Friction will slow it down
46
In which direction does friction act?
Opposite to motion
47
When do you get friction?
1. Between two surfaces in contact
| 2. When an object passes through a fluid
48
What exactly is drag?
Friction which is created when an object passed through a FLUID (e.g. air or liquid)
49
How can drag be reduced?
Streamlining the object
50
How can drag be utilised?
Parachutes have a large surface area to maximise drag.
51
How does the motion of an object affect drag?
As speed increases, so does drag.
52
Why does a car's engine need to work harder to maintain a constant speed at 70mph than at 30mph?
The friction/drag is stronger at 70mph.
53
Explain how objects reach their terminal velocity.
* At first, gravity is greater than the frictional force, so the object accelerates.
* As the speed increases, so does the frictional force, reducing acceleration.
* Eventually, the two become equal and the object doesn't accelerate ay more.
* This is its terminal velocity.
54
What is terminal velocity?
The maximum speed an object can reach when falling.
55
Why would a hammer and feather hit the ground simultaneously on the moon when dropped?
* There's no air
* This means there's no air resistance
* Gravity would make them fall at the same rate
56
What factors affect an object's terminal velocity?
* Mass -> Affects the weight
| * Shape / Surface Area -> Affects the drag
57
How are speed and force related in terms of braking distances?
To stop in a given distance, the faster the vehicle is moving, the bigger the braking force required.
58
What is the stopping distance?
The distance covered by a vehicle between the driver first spotting a hazard and the vehicle coming to a complete stop.
Stopping distance = Thinking distance + Breaking distance
59
What is stopping distance equal to?
Thinking distance + breaking distance
60
What is thinking distance?
The distance the vehicle travels during the driver's reaction time.
61
What is braking distance?
The distance the car travels after the brakes are hit.
62
What factors affect thinking distance?
1. Car speed
| 2. Tiredness, drugs, alcohol, etc.
63
What factors affect braking distance?
1. Car speed
2. Brake quality
3. Tyre quality
4. Grip -> a) Road surface b) Weather c) Tyres
64
What is gravitational force?
The force of attraction between all masses.
65
When is gravity noticeable?
With very large masses, such as a planet.
66
What are the 2 effects of gravity?
1. On the surface of a planet, it makes all things accelerate towards the ground - with the same acceleration of about 10m/s2.
2. It gives everything a weight.
67
What is mass?
The amount of 'stuff" in an object.
68
What is weight?
The force of gravity on an object (which usually depends on the object's mass).
69
With what acceleration does gravity pull things to the Earth?
About 10m/s2.
70
What is the difference between mass and weight?
Mass is the amount of 'stuff' in an object, whereas weight is the force of gravity pulling on the object.
71
What is the unit for weight?
Newtons
72
Is weight a force?
Yes
73
Is mass a force?
No
74
How is weight measured?
Using a spring balance or newton meter.
75
What is the unit for mass?
Kilograms
76
What formula relates mass, weight and gravity?
Weight = Mass x G.F.S.
W = m x g
77
What is the gravitational field strength on Earth?
10 N/kg
78
What is the gravitational field strength on the moon?
1.6 N/kg
79
When a force moves an object through a distance...
... Energy is transferred and work is done.
80
What is the unit for work done?
Joules
81
What is the unit for energy transferred?
Joules
82
What is the unit for gravitational field strength?
N/kg
83
What is the difference between work done and energy transferred?
Nothing, they are the same.
84
What is the equation for work done?
Work done = Force x Distance
W = F x d
(This is also the equation for energy transferred)
85
What is gravitational potential energy?
The energy an object has because of its vertical position in a gravitational field.
86
Why does an object gain gravitational potential energy when it is raised vertically?
Work is done against the force of gravity (i.e. It takes effort to lift it up)
87
What is the unit for gravitational gravitational potential energy?
Joules
88
What is the equation for gravitational potential energy?
Ep = Mass x Gravitational field strength x Height
Ep = m x g x h
89
What is kinetic energy?
The energy of movement.
90
What is the unit for kinetic energy?
Joules
91
What is the equation for kinetic energy?
Ek = 1/2 x Mass x Speed^2
Ek = 1/2 x m x v^2
92
What two factors affect kinetic energy?
1. Speed
| 2. Mass
93
What is the law of conservation of energy?
Energy cannot be created or destroyed.
94
What happens in terms of energy when a car slows down?
The kinetic energy of the car is converted to heat energy by friction between the wheels and the brake pads, causing the temperature of the break pads to increase.
95
When a car is slowing down, what is the kinetic energy transferred equal to?
Kinetic energy transferred = Word done by the brakes
| Energy transferred is the same as work done, remember
96
What is the equation for kinetic energy transferred = work done by breaks?
1/2 x Mass x Velocity^2 = Max. Braking Force x Braking Distance
1/2 x m x v^2 = F x d
(This is because energy transferred = 1/2 x Mass x Velocity^2 and work done = F x d. Energy transferred and work done are equal.)
97
Revise the kinetic energy transferred = work done by brakes equation on pg 25 of revision guide.
Do it!
98
How does speed affect braking distance?
If braking distance is doubled, the distance increased by 4.
(This is because of the v2 in the equation)
99
What happens in terms of energy when an object falls?
* The gravitational potential energy is converted into kinetic energy.
* Some of this kinetic energy is transferred into heat and sound.
100
What happens when a meteor enters the atmosphere and why?
* They meteor has a high kinetic energy
* Friction due to collisions with air particles transfers some kinetic energy to heat energy and work is done
* This increases the temperature and most meteors burn up before reaching the Earth
101
What are meteors that reach the Earth's surface called?
Meteorites
102
How are space shuttles made so that they do not burn up as they enter the atmosphere?
The have heat shields made from special materials which quickly lose energy.
103
What is an elastic object?
An object that returns to its original shape after a force has been applied to it.
104
Describe the energy transfers when a force is exerted on an elastic object.
1. Work is done to change the shape of an elastic object
2. The energy is stored as elastic potential energy
3. When the force is removed, the elastic potential energy is converted to kinetic energy as the object returns to its original shape
105
What is 'k' in elastic object extension calculations?
The spring constant. It depends on the material.
106
What is the equation for the force required to extend an elastic object?
Force = Spring constant x Extension
F = k x e
107
What is spring constant measured in?
N/m
108
What is the limit of proportionality (in terms of elastic objects)?
The maximum force, after which the equation "F = k x e" stops working. After this force, force and extension are no longer proportional.
109
Describe the graph for force against extension.
Force is on the y axis and extension is on the x axis (!)
At first, force and extension are proportional, so there is a straight line. After the limit of proportionality, as force increases, extension increases at an increasing rate.
110
What is power?
The rate of energy transfer / The rate of doing work
111
How does a lever work?
It increases the distance of the force from the pivot, increasing the moment.
112
What are levers known as?
Force multipliers - They reduce the amount of force required to get the same moment.
113
What are some examples of simple levers?
* Wheelbarrow
| * Scissors
114
What happens when the moments acting on an object are not balanced?
There is a resultant moment, which causes the object to turn.
115
What two things give an object stability?
1. Wide base
| 2. Low centre of mass
116
When does an object tip over?
When the centre of mass is outside of the base.
117
Give an example of an object designed to be stable.
A Bunsen burner -> It has a wide, heavy base
118
What is a pendulum's time period?
The time taken for the pendulum from one side to the other and back again.
119
Does a pendulum's time period ever change?
No
120
What is the formula for a pendulum's time period?
Time period (s) = 1 / Frequency (Hz)
T = 1 / f
121
What is the unit for moments?
Newton-metres (Nm)
122
What determines a pendulum's time period?
Its length - the longer the pendulum, the longer the time period.
123
When an object is travelling in a circle does it change velocity or accelerate?
It does both. This is because the object is changing direction, which changes the velocity (and therefore also the acceleration).
124
When an object moves in a circle, in which direction does it accelerate?
Towards the centre of the circle.
125
When an object moves in a circle, in which direction does the resultant force causing it to accelerate act?
Towards the centre of the circle.
126
What is the force that acts towards the centre in circular motion?
Centripetal force
127
What things can cause a centripetal force?
1. Tension
2. Friction
3. Gravity
128
What provides the centripetal force when a car turns on a bend?
The friction from the tyres.
129
What provides the centripetal force when a bucket is whirled around on a rope?
The tension in the rope.
130
What provides the centripetal force in a spinning fairground ride?
The tension in the spokes of the ride.
131
What things affect the size of the centripetal force?
1) Mass
2) Speed
3) Radius
132
How does an object's mass affect the centripetal force?
The larger the mass, the greater the centripetal force.
133
How does an object's speed affect the centripetal force?
The greater the speed, the greater the centripetal force.
134
How does the radius of an object's orbit affect the centripetal force?
The smaller the radius of the orbit, the greater the force (because the object has more turning to do)
135
What is the centripetal force?
The force acting towards the centre of an object's circular orbit, keeping the object in orbit.
136
Are liquid compressible?
No
137
What happens when a force/pressure is applied to a liquid?
The force/pressure is transmitted to other points in the liquid.
138
Pressure in a liquid...
... is transmitted equally in all directions.
139
What is the equation relating force, pressure and area?
Pressure (Pa) = Force (N) / Area (m2)
140
Is power the same thing as force or energy?
No
141
What is a powerful machine?
One which transfers a lot of energy in a short space of time.
142
What is the formula for power?
Power = Work Done (or energy transferred) / Time
P = W/t
143
What is the unit for power?
Watts (or J/s)
144
What is 1 watt equal to?
1 joule transferred per second
145
Give two ways of measuring a person's power output.
1. Timed run upstairs
| 2. Timed acceleration
146
Explain how a timed run upstairs can be used to determine a person's power output.
- The energy transferred is the gravitational potential energy gained (m x g x h)
- The time is the time taken to get up the stairs
- The power is the energy divided by the time
(m x g x h) / t
147
Explain how a timed acceleration can be used to determine a person's power output.
- The energy transferred is the kinetic energy gained (1/2 x m x v2)
- The time is the time taken to accelerate
- The power is the energy divided by the time
(1/2 x m x v2) / t
148
What is a moment?
The turning effect of a force.
149
What is the equation for moment?
Moment = Force x Distance
M = F x d
150
What distance is used in the moment calculations?
The perpendicular distance from the direction of the force to the pivot.
151
In moment calculations, what is done if the force is not perpendicular to the arm being pivoted?
The line of force is extended and a perpendicular line is drawn to the pivot. This is the distance used.
152
When is the maximum moment achieved from a force applied to a spanner?
When the force is perpendicular to the spanner. At any other angle, the distance from the pivot is shorter.
153
What is the centre of mass of an object?
The point at which the whole mass is concentrated.
154
How can the centre of mass of a flat object be found?
1. Suspend the object on a plumb line
2. Draw a line along the plumb line
3. Do the same thing, suspending the shape from a different point
4. The centre of mass is where the two lines cross
155
How can the centre of mass of symmetrical shapes be found?
The lines of symmetry are used.
156
When is an object balanced in terms of moments?
When the total clockwise and anticlockwise moments are equal.
157
How are hydraulic systems usually used?
As force multipliers
158
Explain how a hydraulic system can be used as a force multiplier.
1. Force is applied to a piston with a small surface area
2. This creates a pressure, which is transmitted through the liquid to another piston
3. This piston has a larger surface area, but the pressure is the same, so the force must be greater (P = F/A)
159
Give some examples uses for hydraulic systems.
* Hydraulic car jacks
* Car braking systems
* Deployment of landing gear on some aircraft
