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A-Level Physics > 5. Mechanics > Flashcards

5. Mechanics Flashcards

1
Q

What are the two categories all quantities fall into?

A

scalar, vector

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2
Q

What is the difference between a scalar quantity and a vector quantity?

A

scalar quantities have magnitude only; vector quantities have magnitude and direction

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3
Q

State 7 scalar quantities

A
  • time
  • mass
  • temperature
  • distance
  • length
  • speed
  • energy
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4
Q

State 6 vector quantities

A
  • weight
  • acceleration
  • force
  • displacement
  • velocity
  • momentum
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5
Q

When is an object in equilibrium?

A

when there are no resultant forces and no resultant moments

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6
Q

What is a moment?

A

the force multiplied by the perpendicular distance from the pivot to the line of action of the force

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7
Q

What is the principle of moments?

A

if a system is in equilibrium, the sum of the clockwise moments = the sum of the anticlockwise moments, at any point

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8
Q

What is a couple?

A

a pair of forces of equal size which act parallel to each other but in opposite directions

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9
Q

What is the centre of mass?

A

the single point that you can consider all the weight to act through

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10
Q

What is displacement (s)?

A

distance and direction from starting point in a straight line

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11
Q

What is speed (v)?

A

how fast something is going regardless of direction

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12
Q

What is velocity (v)?

A

how fast something is going with direction

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13
Q

What is acceleration (a)?

A

the rate of change of velocity

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14
Q

What does the gradient of a displacement-time graph represent?

A

velocity

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15
Q

What does the gradient of a velocity-time graph represent?

A

acceleration

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16
Q

What does the area under a velocity-time graph represent?

A

change of displacement

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17
Q

What does the area under an acceleration-time graph represent?

A

change in velocity

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18
Q

What is Newton’s first law of motion?

A

if there are no resultant forces acting on a object it will either:

  • stay at rest
  • travel at a constant speed in a straight line (constant velocity)
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19
Q

What is Newton’s second law of motion?

A

“the acceleration of an object is proportional to the resultant force acting on it”

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20
Q

What is the equation representing Newton’s second law?

A

F = ma

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21
Q

What is Newton’s third law of motion?

A

“if object A exerts a force on object B, then object B exerts an equal but opposite force on object A”

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22
Q

How can you find the centre of mass of a flat object?

A
  • hang the object freely from a point
  • draw a vertical line downwards from the point of suspension
  • use a plumb bob to get the line exactly vertical
  • hang the object from several different points, and draw vertical lines
  • the centre of mass is where the line cross
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23
Q

When will can object topple over?

A

if the line of action of the objects weight falls outside its base area

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24
Q

What is freefall?

A

the motion of an object undergoing an acceleration of ‘g’

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25
What is friction?
- a force that opposes motion | - turns kinetic energy into thermal energy
26
What are the two main types of friction?
- contact friction | - fluid friction
27
When does contact friction happen?
between solid surfaces
28
What is fluid friction also known as?
- drag - fluid resistance - air resistance
29
What is fluid friction caused by?
a gas or a liquid
30
What three factors affect drag?
- viscosity of the fluid - speed - surface area of profile
31
What is the relationship between drag and speed?
drag is directly proportional to speed squared
32
What is lift?
an upwards force on an object moving through a fluid
33
How does lift occur?
lift happens when the shape of an object causes the fluid flowing over it to change direction
34
What direction does lift act in comparison to the direction of fluid flow?
perpendicular
35
What direction does drag act in comparison to the direction of fluid flow?
parallel
36
When does terminal velocity occur?
when the frictional forces on an object are equal to the driving forces on an object
37
What are the two main ways of increasing a vehicle’s maximum speed?
- increasing the driving force | - reducing the frictional force
38
How are momentum, mass and velocity related?
momentum = mass x velocity
39
Is momentum a scalar or vector quantity?
vector
40
What is the principle of conservation of linear momentum?
the total momentum before a collision = the total momentum after a collision, provided no external forces act
41
What is an elastic collision?
a collision where both momentum and kinetic energy are conserved
42
What is an inelastic collision?
a collision where momentum is conserved but kinetic energy is not conserved
43
Are most real life collisions elastic or inelastic?
inelastic
44
What must be applied for a change in momentum to occur?
a force
45
What is the relationship between force, change in momentum and time?
force = change in momentum / time
46
What is impulse?
the product of force and time
47
What is impulse equal to?
change in momentum
48
What are the units of impulse?
Ns or kgms^-1
49
What does the area under a force against time graph equal?
- the impulse | - the change in momentum
50
What three things in a car increase the duration of impact and hence decrease the size of the force when change in momentum is conserved?
- crumple zones - seat belts - air bags
51
How do crumple zones decrease the size of the force on a passenger?
deform plastically (permanently) on impact, causing the car to take longer to stop, increasing the impact time and decreasing the force on the passengers
52
How do seat belts decrease the size of the force on the passenger?
stretch slightly, so they increase the impact time for the wearer, reducing the force acting on their chest
53
How do air bags decrease the size of the force on the passenger?
slow down the passengers more gradually, and prevent them from hitting hard surfaces inside the car
54
When is work done?
when energy is transferred
55
What is the equation linking work done, force and distance?
work done = size of force in direction of travel x distance travelled
56
How is work done calculated when the force and direction of travel aren’t parallel?
work done = force x cos(angle between force and direction of travel) x distance
57
What is the area under a force against distance graph equal to?
work done
58
What is power?
rate of doing work
59
What are the units of power?
Watts
60
How is power calculated?
power = change in work done / time
61
What is the equation linking power, force and velocity?
power = force x velocity
62
What is the principle of conservation of energy?
- energy cannot be created or destroyed - it can only be transferred from one form to another - but the total amount of energy in a closed system will not change
63
What is efficiency?
a way to quantity how much of the energy (or power) put in is transferred into useful energy (or power)
64
How is efficiency calculated?
efficiency = ((useful energy/power out) / (total energy/power in)) x 100
65
How do you calculate kinetic energy?
1/2 x mass x velocity^2
66
How do you calculate gravitational potential energy?
mass x gravity x height

A-Level Physics (15 decks)

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