Forces And Motion Flashcards
(132 cards)
1
Q
What is a scalar quantity?
A
Only has a magnitude
2
Q
What is magnitude?
A
Size or extent of something
3
Q
Examples of scalar quantities
A
Speed
Distance
Charge
Temperature
Time
4
Q
What are the units of speed?
A
m/s
5
Q
What are the units for distance?
A
Metres (m)
6
Q
What is a vector quantity?
A
Has both magnitude and direction
7
Q
Examples of vector quantities
A
Velocity
Displacement
Acceleration
Any force
8
Q
What are the units for velocity?
A
m/s (direction)
9
Q
What are the units for displacement?
A
metres (m) (direction)
10
Q
Equation for speed
A
Distance travelled (d)
—————————
Time taken (t)
11
Q
Equation for velocity
A
Displacement (s)
————————
Time taken (t)
12
Q
What does ‘s’ stand for?
A
Displacement
13
Q
What is acceleration?
A
The rate of change in velocity
(How quickly something speeds up or slows down)
14
Q
Equations for acceleration
A
a = change in velocity/time
(2 x a x s) = v2 - u2 / v2 = u2 + (2 x a x s)
15
Q
What does ‘v’ mean?
A
Final velocity
16
Q
What does ‘u’ mean?
A
Initial velocity
17
Q
What is the initial velocity if an object accelerates from stationary?
A
0
18
Q
What do distance-time graphs show?
A
How far something has travelled in a certain period of time
19
Q
What does the gradient at a specific point on a distance-time graph tell us?
A
The speed the object is travelling at that time
20
Q
What is on the y-axis on a distance-time graph?
A
Distance (m)
21
Q
What is on the x-axis on a distance-time graph?
A
Time (s)
22
Q
What does a straight steeped line on a distance-time graph mean?
A
Object is moving at a CONSTANT SPEED
23
Q
What does a flat line on a distance-time graph mean?
A
Object is STATIONARY (not moving)
Gradient = 0
24
Q
What does an increasing curve upwards on a distance-time graph mean?
A
Object is ACCELERATING (speed increasing)
25
What does a decreasing curve downwards on a distance-time graph mean?
Object is DECELERATING (speed decreases)
26
How do you find the gradient of a flat line on a distance-time graph?
Change in distance
—————————
Change in time
27
How do you find the gradient of a curved line on a distance-time graph?
1) draw a tangent at the point
2) draw two points on the tangent
3) draw dotted lines from each horizontal and vertical
Use the equation:
Change in distance
—————————
Change in time
28
What does a velocity-time graph show?
How an object’s velocity changes overtime
29
What does the gradient on a velocity-time graph tell us?
The acceleration
30
What is on the y-axis on a velocity-time graph?
Velocity (m/s)
31
What is on the x-axis on a velocity-time graph?
Time (s)
32
Equation for acceleration (velocity-time graph)
Change in velocity
—————————
Change in time
33
What are the units for acceleration?
m/s squared
34
What does a straight steeped line (constant positive gradient) on a velocity time graph mean?
Object has a constant acceleration
35
What does a flat line on a velocity time graph mean?
Object has a constant velocity
36
What does an increasing curve upwards on a velocity time graph mean?
Rate of acceleration is increasing
37
What does a decreasing straight curve downwards (constant negative gradient) on a velocity-time graph mean?
Object has a constant deceleration
38
How do you find the distance travelled on a velocity-time graph?
Area under the line (m)
39
What is Newton’s 1st Law?
A resultant force is required to change the motion of an object
40
What happens when an object is stationary and the resultant force is 0?
The object remains stationary
41
What happens when an object is moving and the resultant force is 0?
The object will carry on moving at the same velocity
42
What is Newton’s 2nd Law?
A resultant force will cause an object to accelerate in the direction of the force
43
If the resultant force is to the right what will happen to the object?
It will accelerate to the right
44
What happens if an object is stationary and the resultant force is to the right?
It will start moving (to the right)
45
What happens if an object is moving to the right and the resultant force is to the right?
It will speed up
46
What happens if an object is travelling left and the resultant force is to the right?
It would slow down
47
What happens if an object is moving slowly to the left and the resultant force is to the right?
Slows down even more and will probably stop moving
48
What could a resultant force to the right do to an object?
Make it change direction but keep the same speed
49
Does the speed of the moon when orbiting the earth change or remain constant?
Remains constant
50
Does the direction of the moon when orbiting the earth change or remain constant?
Always changes
51
Why is the velocity of the moon always changing if the speed is always constant?
Any change to the direction means a change in velocity
—> the direction of the moon is always changing
52
Why does the moon’s direction keep changing as it orbits the earth?
The earth’s mass exerts a gravitational pull on the moon (pulls it towards the earth)
This force is always perpendicular to the moon’s motion
—> makes the moon change direction as it moves around the Earth
53
The size of the resultant force is …?
Directly proportional to the acceleration it causes
E.g. if the resultant force was twice as big then the acceleration that it causes would also be twice as big
54
Equation for resultant force
F = ma
55
What does ‘F’ stand for?
Resultant force
56
What does ‘m’ stand for (F = ma)?
Mass
57
What are the units for mass?
Kg
58
What are the units for the resultant force?
Newtons (N)
59
What does inertia mean?
The tendency for the motion of an object to remain unchanged unless acted upon by a resultant force
(Newton’s 1st Law)
60
How fast are sound waves in air?
330 m/s
61
What happens to the speed of sound waves in different mediums?
It changes
62
What does anything dropped fall at?
10 m/s squared
63
What does an object’s inertial mass measure?
How difficult it is to change an object’s velocity
64
Equation for inertial mass
Force
——————
Acceleration
65
Does a larger mass have a little or a lot of inertia?
A lot
66
Why do large mass’ have a lot of inertia?
It requires a really big force to change its velocity
67
Large mass’ have quite a small …?
Acceleration
68
What is Newton’s 3rd Law?
When two objects interact, the forces they exert on each other are EQUAL and OPPOSITE
69
In Newton’s 3rd Law what does equal refer to?
The magnitude of the two forces
70
In Newton’s 3rd Law what does opposite refer to?
Direction
71
If you pushed a force of 100N on a box what would happen?
The box would also exert an equal force of 100N on you
72
What is the normal contact force?
The force that acts perpendicular (upwards) from a surface when an object is in contact with it and it supports the weight of the object
73
What is friction?
The force that acts parallel (sideways) to the surface and opposes the motion or attempted motion between two touching surfaces
74
What would happen if you tried to push a small box?
It would move (has a lower mass than you)
75
What would happen if you tried to push a really big box fast?
It wouldn’t move and you might be pushed backwards (has a bigger mass than you)
76
What would happen if you tried pushing a medium sized box?
You might get pushed backwards a little but the box might still move forwards
77
What do you need to move an object?
Either a high force or a small mass (why the smaller object will generally move most)
78
Equation linking acceleration, force and mass
a = F/m
79
What are free body diagrams?
Simple diagrams which show all of the forces that are acting on an object
80
Are forces scalar or vector quantities?
All are VECTORS (both have a magnitude and direction)
81
In free body diagrams what will some forces acting in opposite directions do?
Will balance out and so cancel out
82
What is the resultant force?
The overall force acting on an object, taking into account all the different forces acting on it
83
Equation for weight
W = mg
84
What are the units for weight?
Newtons (N)
85
What are the units for gravitational field strength?
N/Kg
86
Why is gravity less on the moon?
The moon has a lower mass
87
What is used to measure mass?
Mass balance
88
What is used to measure weight?
Newton meter
89
What is the upwards force when someone is sitting down?
The normal contact force
90
When is the resultant force on an object at zero?
1) the object remains at rest
2) the object is moving at a constant velocity (fixed speed and direction)
91
What happens if all the forces on an object balance out?
The resultant force is 0 and the object is in equilibrium
92
What is terminal velocity?
The constant speed a falling object reaches when the air resistance force is equal to its weight so there is no more acceleration
93
Mass is always the …?
Same
94
When does weight change?
If the gravitational field strength changes
95
What is air resistance?
An upwards force that opposes the motion or weight (if falling) of an object through air
96
What causes air resistance?
The air particles colliding with a moving object which creates a force that slows it down
97
What does air resistance do to a person?
Slows them down
98
What does the size of the air resistance depend on?
Surface area
Velocity
99
The faster they’re moving the …?
More particles they will collide with so the bigger the air resistance
100
Why does the resultant force become smaller when falling?
Air resistance and weight are acting in opposite directions so the air resistance will cancel out some of the weight
101
Why does air resistance increase when the person’s velocity increases?
There colliding with more particles so air resistance increases
102
How does a skydiver reach terminal velocity?
1) when they first jump out the only force acting on them is their weight, so they accelerate downwards
2) as their speed increases, air resistance increases
3) eventually the air resistance becomes equal to the weight and so the forces are balanced so there is no resultant force
4) the skydiver falls at a constant speed and so they have reached terminal velocity
5) when they open the parachute their surface area increases and so the air resistance suddenly increases
6) now the air resistance is greater than the weight so the skydiver decelerates (slows down)
7) as they slow down the air resistance reduces until it becomes equal to their weight again and the skydiver will reach a new, lower terminal velocity
103
What 3 things could happen to an object when you apply force to it?
Compress
Stretch
Bend
104
What is deformation?
The change in shape of an object as a result of forces being applied to it
105
What is elastic deformation?
If the object does return to its original shape after the forces have been removed
106
What is inelastic deformation?
If the object does not return to its original shape after the forces have been removed
(Stays deformed)
107
What is extension?
The increase in length of a spring when it’s stretched
108
What happens when you add more mass to a spring?
The extension increases proportionally
109
Equation linking force and extension
F (loop) e
110
What is a spring constant?
The measure of how many Newtons of force it would require to stretch or compress the object by 1 metre
111
Equation for Hooke’s Law
F = ke
112
What does ‘k’ stand for?
Spring constant
113
What are the units of the spring constant?
N/m
114
What are the units for extension?
Metres (m)
115
The higher the spring constant …?
The stiffer the material
116
Why do stiffer materials have a higher spring constant?
They require more force to stretch
117
What is Hooke’s Law?
An object’s extension is directly proportional to the force applied
118
What type of deformation occurs in Hooke’s Law?
Elastic deformation
119
What can happen if you stretch an object too much?
It could pass its elastic limit (limit of proportionality) and will be inelastically deformed
120
What is the elastic limit also known as?
The limit of proportionality
121
What does stopping distance mean?
The total distance a vehicle travels from the moment when the driver first notices an obstruction to when the vehicle comes to a stop
- the sum of the thinking distance and the braking distance
122
Stopping distance = …?
Thinking distance + braking distance
123
What is the thinking distance?
The distance a vehicle travels while the driver is reacting before applying the brakes
124
What two things affect thinking distance?
Speed
Reaction time
125
How does speed affect thinking distance?
The faster your going the further you’ll travel while reacting
126
How does reaction time affect thinking distance?
The driver’s reaction time will slow down if:
They’re tired
Consumed alcohol/drugs
Distracted
127
What is the braking distance?
The distance a vehicle travels after the brakes are applied until it comes to a stop
128
What 2 things increase the vehicle’s kinetic energy?
Speed
Mass
129
What increases the braking distance?
Worn brakes
Worn tyre tread
Ice on the road (less friction)
130
What affects both the thinking and braking distances?
The speed of the vehicle
131
Equation for velocity squared (v2)
v2 = u2 + 2as
132
Equation for extension
Stretched length - the original unstretched length
