Mechanics Flashcards
(97 cards)
1
Q
What is a scalar quantity?
A
A quantity that has magnitude (size) BUT NOT DIRECTION
2
Q
Give 3 examples of scalar quantities
A
- Mass
- Time
- Energy
- Temperature
- Power
- Density
- Pressure
- Speed
- Distance
3
Q
Can scalar quantities be positive and negative?
A
Yes
4
Q
What is a vector quantity?
A
A quantity that has both magnitude AND direction
5
Q
Give 3 examples of vector quantities
A
- Force
- Velocity
- Acceleration
- Displacement
- Momentum
6
Q
Can vector quantities be positive and negative?
A
Yes, but always with reference to a direction being defined as the positive edirection
7
Q
What is the difference between distance and displacement?
A
- Distance is a scalar quantity an displacement is a vector quantity
- Distance is the magnitude of displacement
- Displacement is distance is a particular direction
8
Q
What is the difference between speed and velocity?
A
- Speed is a scalar quantity and velocity is vector quantity
- Speed is the magnitude of velocity
- Velocity is speed in a particular direction
9
Q
What is an equation linking speed, distance time?
A
Speed = distance / time
speed: ms-1
distance: meters (m)
time: seconds (s)
10
Q
What is the equation for velocity?
A
Velocity = change in displacement / time
Velocity: ms-1
Displacement: meters (m)
time: seconds (s)
11
Q
When do you use the equations s=d/t and v=displacement/t?
A
When speed/ velocity is constant
12
Q
What is the equation for acceleration?
A
acceleration = change in velocity/ time
acceleration: ms-2
velocity: ms-1
time: seconds (s)
13
Q
When can the equation for acceleration be used?
A
When the acceleration is constant
14
Q
What does the gradient of a distance- time graph represent?
A
speed
15
Q
What does the gradient of a displacement-time graph represent?
A
Velocity
16
Q
What does the gradient of a Velocity-time graph represent?
A
acceleration
17
Q
What does the area under a speed-time graph represent?
A
Distance
18
Q
What does the area under a velocity-time graph represent?
A
Displacement
19
Q
What does the area below a velocity-time graph represent?
A
displacements in the negative direction
20
Q
What does a steeper gradient on a displacement-time graph represent?
A
The steeper the gradient the greater the speed
21
Q
What does a positive gradient represent on a displacement-time graph?
A
Velocity in the positive direction
22
Q
What does a negative gradient represent on a displacement-time graph?
A
Velocity in the negative direction
23
Q
What does a gradient of 0 represent on a displacement-time graph?
A
0 velocity
24
Q
What does a steeper gradient on a velocity-time graph represent?
A
The steeper the gradient, the greater the magnitude of the acceleration
25
What does a positive gradient represent on a velocity-time graph?
Acceleration in the positive direction
| i.e. "speeding up"
26
What does a negative gradient represent on a velocity-time graph?
velocity in the negative direction
| i.e. "slowing down"
27
What does a gradient of 0 represent?
acceleration is 0
| i.e. Constant velocity
28
What does a "positive area" represent on a velocity-time graph
A displacement in the positive direction
29
What does a "negative" area represent on a velocity-time graph?
A displacement in the negative direction
30
How do you find the total displacement from a velocity-time graph?
Add together individual displacements, after making every negative area positive
31
What is the equation for average speed?
Average speed = total distance / total time
32
What is the equation for average velocity?
Average velocity = net change in displacement / total time
33
What is the equation for average acceleration?
Average acceleration - net change in velocity / total time
34
What equations can be used for questions where acceleration is uniform?
SUVAT
v=u+at
s=1/2(u+v)t
v2 - u2=2as
s: displacement(m)
u: initial velocity(ms-1)
v: final velocity(ms-1)
a: acceleration(ms-2)
t: time(s)
35
What is a force?
The application of a push or pull to an object by another object
36
What type of quantity is a force?
VECTOR quantity
| - it has magnitude AND direction
37
What is the unit for force?
newtons (N)
38
What causes weight to be applied? What does the magnitude of the force depend on? What direction does it act in?
- Caused by mass in a gravitational field
- depends on "mass" and "gravitational field strength"
- Acts downwards
39
What causes normal contact to be applied? What does the magnitude of the force depend on? What direction does it act in?
- Caused by 2 solid objects in contact with each other
- NOT DEPENDENT ON ANY OTHER FACTOR
- Acts perpendicular to the surface of contact
40
What causes drag to be applied? What does the magnitude of the force depend on? What direction does it act in?
- Caused by the movement of an object through a fluid
- Depends on "speed" and "cross- sectional area"
- Acts in the opposite direction to relative motion
41
What causes friction to be applied? What does the magnitude of the force depend on? What direction does it act in?
- Caused by relative sliding motion between 2 solid surfaces
- Depends on the "nature of the surface" i.e. if it is smooth/rough
- Acts in the opposite direction to relative motion
42
What causes a magnetic force to be applied? What does the magnitude of the force depend on? What direction does it act in?
-Caused by 2 magnets or a current in a magnetic field
-Depends on the "magnetic field strength" and "current in the wire"
-Acts perpendicular to current in wire
LIKE poles REPEL
OPPOSITE poles ATTRACT
43
What causes an electrostatic force to be applied? What does the magnitude of the force depend on? What direction does it act in?
-Caused by 2 charges or a charge in an electric field
-Depends on the "electric field strength"
-LIKE charges REPEL
OPPOSITE charges
ATTRACT
44
What causes upthrust to be applied? What does the magnitude of the force depend on? What direction does it act in?
- Caused by a solid immersed in a fluid
- Depends on the "weight of fluid that is displaced"
- Acts upwards
45
What causes thrust to be applied? What does the magnitude of the force depend on? What direction does it act in?
- Caused by the driving force from an engine
- Depends on the "power of the engine"
- Acts in the direction of propulsion (a push/pull)
46
What causes lift to be applied? What does the magnitude of the force depend on? What direction does it act in?
- Caused by an aerofoil (wing) moving through a fluid
- Depends on "speed", "density of fluid" and "wing shape"
- Acts perpendicular to wing
47
What causes tension to be applied? What does the magnitude of the force depend on? What direction does it act in?
- Caused by materials being stretched: e.g, spring/ string/ wire, etc
- Depends on "extension"
- Acts along the strong/ spring or wire
48
What is the resultant force?
The overall force acting on an object
(All the forces can be replaced by this single force/ has the same effect)
however, IT IS NOT A SEPARATE PHYSICAL FORCE
49
What is tension?
The force that is transmitted through a cable/wire/rope when it is pulled
50
What is permanent extension?
The increase in length from the original/ unstretched length, after it has been pulled
51
On a force-extension graph, what does the gradient/ steepness indicate?
The steeper the graph, the MORE FORCE is required to produce a given extension
52
What does it mean if a material is "rigid"?
-Deformation is 0/ so small it is negligible (even with a large tension force)
53
How can you tell how rigid a material is from a force-extension graph?
A material that is more rigid, will only extend slightly/ requires a lot of force to extend slightly, before breaking
54
What happens if a spring is pushed in by equal forces on each side?
- Spring undergoes compression forces
| - results in contraction rather than extension
55
What is elastic enxtension?
The extension is ELASTIC if the spring/ wire is stretched by a tension force and it returns to its original length when the tension force is removed
56
what is inelastic extension?
The extension is INELASTIC if the spring/ wire is stretched by a tension force and it DOES NOT return to its original length when the tension is removed
57
What does it mean for a material to be ductile
The material can undergo permanent stretching
58
What is the elastic limit?
The point on the force-extension graph where the extension goes from being elastic to inelastic
59
What is Hooke' law?
The extension of an elastic object is directly proportional to the force applied to it
60
What equation applies for objects that obey Hooke's law?
F = kx
F(Force): newtons (N)
k(spring constant): Nm-1 OR (Ncm-1, kNm-1 - depends on the units used for force and extension)
x(extension): metres (m)
61
What is the spring constant?
It is a measure of rigidity - materials with HIGH spring constants require LARGE FORCES to produce SMALL extensions
(therefore, it is also the gradient of force-extension graphs)
62
What is the limit of proportionality?
The point beyond which the force applied to an object is no longer proportional to its extension.
63
What factors affect the spring constant? How?
-Cross-section area
The greater the cross-sectional area, the greater the spring constant
-Length of wire/spring
The longer the wire, the smaller the spring constant
64
If 2 identical springs, each of spring constant k, are connected in SERIES what is the new spring constant?
-The same force produces double the extension so the spring constant is halved
= 1/2k
65
If 2 identical springs, each of spring constant k, are connected in PARALLEL what is the new spring constant?
-Double the force will be needed to produce the same extension so the spring constant is doubled
= 2k
66
What does the area under a force-extension graph represent?
The total area represents the work done by the tension force when a spring/ wire is extended
ALSO, ONLY FOR THE AREA UNDER THE GRAPH WHERE THE ELASTIC LIMIT HAS NOT BEEN EXCEEDED- this represents the elastic potential energy
- this is known as retrievable energy
67
What is the formulae for the energy stored in a stretched string/ wire, provided it obey's Hooke's law and has not exceeded the elastic limit
```
E = 1/2 Fx = 1/2kx2
(x squared)
Energy: joules(j)
F(Force): newtons (N)
k(spring constant): Nm-1
x(extension): metre(m)
```
68
What is newtons first law?
A bod will remain at rest or in a state of uniform motion in a straight line unless acted on by a resultant external force
-Unless there is a resultant force on an object, that object WILL NOT ACCELERATE?
69
What happens to an object that has balanced forces?
it IS NOT ACCELERATING
could be stationary
OR
traveling with uniform/ constant velocity
70
What affect does mass have to a change in motion?
Mass resists a change in motion (acceleration)
- The larger the mass of an object, the greater the force needed to cause a given acceleration
- This property of mass is known as inertia
71
What is the difference between weight and mass?
Mass is just a measure of how much "stuff" (matter) an object is made up of - is the same on the earth and the moon
[Kg]
Weight is the force of gravity on an object- the weight is different on the earth and moon
72
Why is the force of gravity bigger on the earth than it is on the moon?
Every physical object has its own gravitational field
- bigger objects have a stronger gravitational force
- the mass of the earth is much greater
73
What is the equation for working out weight?
W = mg
Weight: Newtons (N)
Mass: Kilograms (Kg)
Gravitational force can vary- on EARTH it is 9.81N/Kg Or 9.81ms-2
74
What is the equation represents Newtons second law
```
F = ma
"The acceleration of an object is dependent on its mass and net force acting on the object"
Resultant force: newtons (N)
Mass: Kilograms (Kg)
Acceleration: N/kg or ms-2
```
75
What is newtons third law?
"If body A exerts a force on body B then body B exerts an equal and opposite force of the same type, on body A"
76
What happens to the acceleration of an object that is free-falling? Why?
- An object that is in free-fall is falling due to gravity & has no other forces acting on it except weight
- So the resultant force is equal to weight
- F = W = mg
- So a=F/m changes to a=mg/m which just means for an object under free-fall, the acceleration is equal to the gravitational field strength
77
What factors affect air resistance?
- Speed: The magnitude of the air resistance force increases with increasing speed of motion
- Cross-sectional area of the object: As the cross-sectional area increases, the air resistance increases
78
What is firction?
A force that slows down moving objects
79
If an object is accelerating, what does that tell you about the pushing force vs the friction acting on the object?
- If an object is accelerating
- there is a resultant force
- The pushing force in not equal to the force of friction
80
What is the relationship between friction and speed?
Friction increases as speed increases
81
What is terminal velocity/ how does an object reach terminal velocity?
- When an object falls due to gravity it experiences 2 main forces: Weight and Air resistance
- Weight is CONSTANT and air resistance INCREASES with speed
- When the object first falls it experiences an initial acceleration equal to g
- However as the object accelerates, the air resistance increases
- This decreases the resultant force downwards
- Therefore the acceleration decreases
- Eventually the air resistance becomes equal to the weight
- At this point the resultant force becomes 0; can no longer go faster
- The speed at which the air resistance = the weight is called the terminal velocity
82
What is meant by the term momentum? what equation is used to represent this?
"The momentum of an object is the product of the mass and velocity of the object"
: p = m v
Momentum: Kgms-1 or Ns
Mass: kilograms (Kg)
Velocity: ms-1
83
Is momentum a vector or scalar quantity?
VECTOR:
-the momentum of an object is in the same direction as its velocity
and a direction must always been given with the value of momentum
e.g: p = 0.30Kgms-1 to the left
84
What is the law of conservation of momentum in calculations in 1 dimension?
In any closed system involving the interaction between 2 (or more) objects, the total momentum of the system BEFORE the interaction is equal to the total momentum of the system AFTER the interaction
85
What can happen to a system to make it no longer a closed system?
The action of an external resultant force on an object will mean the system is no longer closed; the momentum will change
86
How do you work out momentum, when the system is no longer closed/ an external force is applied?
momentum = external resultant force x time
87
What equation links force, momentum and time?
Force = rate of change of momentum
i.e: Force = change in momentum/time
88
What is work?
The energy transferred to or from an object, hen a force acts on the object and moves it through a distance in line with the force
89
What is the equation for work?
work = force x distance (in direction of force)
work: Nm or joules(J)
force: N
distance: m
90
Is work a vector or scalar quatity?
SCALAR
however it can have a + or - sign
91
What is the equation for gravitational potential energy?
gravitational potential energy = mgh
potential energy: joules (J)
mass: Kilogram (Kg)
g: Nkg-1
height: (m)
92
What is the equation for kinetic energy?
kinetic energy = 1/2mv2
kinetic energy: joules (J)
mass: kilogram (Kg)
velocity: ms-1
93
What are the 2 equations for power?
Power = energy transfer/time
OR
Power = work done/ time
power: watts(W) or Js-1
energy : joules (J)
time: seconds (s)
94
What is the law of conservation of energy?
Energy is never created or destroyed; it is only transferred from on form to another
95
What is meant by the term potential energy?
Energy that is stored in some form for future use
| e.g: chemical potential energy, gravitational potential energy, etc
96
What is the difference between USEFUL energy and WASTED energy?
- Useful energy is energy that is converted into the form for which the device is intended
- Wasted energy is energy that is converted into forms of energy other than that for which the device is intended
97
What is the equation used to calculate percentage efficiency?
percentage efficiency = [useful output/ total input] x 100
efficiency: left as a fraction/ percentage
