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Mechanics Flashcards

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1
Q

What is the difference between mass and weight?

A

Mass is scalar and not dependent on gravity acting upon it

Weight is vector and dependent on gravitational field strength

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2
Q

If an object is in equilibrium, it means the object is….

A

Not accelerating so is either:
-stationary
-moving at a constant velocity

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3
Q

How can forces acting on an object be shown to be in equilibrium?

A

-Adding horizontal and vertical components of the forces acting on it, showing they equal 0

-If there are 3 forces acting on the object draw a scale diagram -> closed triangle = equilibrium

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4
Q

What is a moment?

A

A turning force: force multiplied by the perpendicular distance from the point to the line of action of the force

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5
Q

What is meant by a couple?

A

A pair of equal and opposite coplanar forces

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6
Q

What is meant by the centre of mass?

A

The point at which all the mass of an object acts

For a uniform object the centre of mass is the centre of the object

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7
Q

If you have a uniform object, where would its centre of mass be?

A

At the centre of the solid

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8
Q

What is the area under a velocity-time and acceleration-time graph?

A

The displacement travelled and the velocity respectively

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9
Q

As speed increases, air resistance…

A

Increases (proportional to the square of speed)

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10
Q

A ball is projected off a castle at 6 m/s, how does its horizontal velocity change from its launch until it hits the ground?

A

Horizontal velocity stays the same -> no acceleration in that direction

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11
Q

How do SUVAT equations reflect that all objects fall at the same rate?

A

Mass is not included in SUVAT -> mass of an object doesn’t affect its speed or acceleration

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12
Q

In projectile motion, what is vertical acceleration?

A

Vertical acceleration + gravitational field strength

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13
Q

What is meant by terminal velocity?

A

When forces acting on a falling object become balanced
Acceleration becomes 0, and object is moving at max. velocity

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14
Q

What is meant by friction?

A

A resistive motion between an object and a surface or an object moving through a fluid
Acts in the opposite direction to the movement

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15
Q

What is Newton’s 2nd law?

A

Acceleration is proportional to force
F=ma

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16
Q

What is Newton’s 1st law?

A

An object stays moving at a constant velocity until an external resultant force acts upon it

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17
Q

What is Newton’s 3rd law?

A

If an object A exerts a force on object B, Object B will exert an Equal but opposite force on object A

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18
Q

What is the principle of moments?

A

When a body is balanced
total clockwise moments = total anticlockwise moments (about the same point)

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19
Q

How do you find a resultant vector?

A

How you do it in maths. Add the two vectors and use Pythagoras.

You need a bearing too.

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20
Q

A Remote controlled aeroplane flies with a velocity 14ms-1 east with an 8.0ms-1 wind north. Find resultant vector

A

142 + 8.02 = R2 so root answer = 16.124

Use tan-1(8.0/14) to find angle of 30º

Barings are measured from the north so 90-30 = 060

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21
Q

What is a free-body diagram?

A

A single body on its own showing all the forces acting on IT but not the forces it exerts on the rest of the world.

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22
Q

Define equilibrium

A

If an object is in equilibrium there is no resultant force
There are also no resultant moments

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23
Q

Explain how a lever works

A

A lever increases the perpendicular distance from a turning point / pivot so with the same force you get a larger moment.

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24
Q

What is a couple? What makes them special?

A

a pair of forces equal in size but acting in opposite directions. A couple causes no resultant linear force but does produce a moment.

25
Q

Unit for a moment

A

Nm

26
Q

Define displacement

A

How far an object’s travelled from its starting point in a given direction

27
Q

What is the gradient of a Velocity-Time graph?

A

Acceleration
(Rate of change of velocity)

28
Q

What is shown by the area under a speed-time graph?

A

distance

29
Q

What is shown by the area under a velocity-time graph?

A

displacement

30
Q

What are the advantages of using a data logger over a traditional method to calculate velocity-time graphs?

A

Higher sampling rates
More accurate data - no reaction times
real-time data display

31
Q

What is the area under an acceleration time graph?

A

total ∆V

32
Q

What is freefall?

A

When gravity acting on an object and nothing else

33
Q

All objects fall to the ground _____ assuming no drag or contact friction.

A

At the same rate

34
Q

Describe the experiment to determine g using freefall

A
  • As you flick switch electromagnet lets go and timer starts.
  • its a ball baring so we can ignore air resistance as it is minimal
  • ball hits trapdoor and timer stops
  • repeat each height 3 times, take an average

Plot a graph of H against T2 gradient = ∆s/∆t2 = 1/2g so x 2

s = 1/2at2

35
Q

What is a projectile?

A

Any object with an initial velocity free to move under gravity.
Horizontal velocity remains unchanged
Verticle decreases due to g

36
Q

What would considering air resistance do to the path of a projectile?

A

Causes drag = opposite direction to motion.

If it has a verticle component it decreases the max height
if it has a horizontal component it decreases the max X displacement

37
Q

3 key ideas about friction

A

-Always opposes motion
-Never speeds up only slows down
-Ke becomes heat

38
Q

What’s lift? What causes it?

A

An upwards force on an object moving through a fluid. It happens when the shape of an object causes the fluid flowing over it to change direction

39
Q

What is terminal speed (velocity)?

A

The speed that an object reaches when it falls through a gas or liquid and the forces acting on it are balanced
( no longer accelerating )

40
Q

Compare elastic and inelastic collisions

A

Inelastic = Ke NOT conserved
Elastic = Ke perfectly conserved

41
Q

In an inelastic collision, Ke is _____ and Momentum is ________

A

Not conserved / Conserved.

42
Q

Define impulse

A

The product of force and time

43
Q

What is under a force-time graph?

A

Impulse

44
Q

How can we reduce the force of an impact.

A

Force = rate of change of momentum.

So if we increase the time of the impact we reduce the force.

45
Q

How does a car take advantage of force being the rate of change of momentum in terms of safety?

A
  • Crumple zones - increase time of impact decreasing overall force felt
  • Seat belt - stretch slightly increasing the time taken for the wearer to stop reducing force
  • Air bag - same thing
46
Q

Define work

A

W = Force x distance measured in joules.

47
Q

Power =

A

Rate of change of energy transfer, 1 watt = 1 joul per second.

48
Q

What’s under a force-displacement graph?

A

WORK DONE

49
Q

Link power force and velocity

A

Power = Force x velocity

50
Q

Link power force and velocity

A

Power = Force x velocity

51
Q

State the principle of conservation of energy

A

Energy cannot be created or destroyed. Only transferred from one form to another. Total energy in a system doesn’t change.

52
Q

Apply Newton’s 1st and 2nd laws on shooting a bullet (projectile motion)

A

1st - no significant forces acting in the horizontal direction -> bullet will continue to have the same horizontal v

2nd - only force acting on the bullet is weight (acting downwards)
Weight = m x a
m g = m a
g = a = 9.81 ms-2

53
Q
A
  • falls -> accelerates downwards, gaining speed with each second
  • increase in speed -> increase in air resistance

-As falls faster and faster, air resistance increases until it = the force of gravity

-Once air resistance = gravity, forces balanced and skydiver no longer accelerates. The skydiver is said to have reached a terminal velocity.

54
Q

Why is impulse more useful that only knowing the force?

A

Because impulse = Δ momentum

f t = mv - mu

55
Q

In an elastic collision, KE is ___________

In an inelastic collision, KE is ___________

In an explosion, KE is ___________

A

conserved / lost (transferred to another energy store) / gained (from another store)

56
Q

Momentum is a _______ and therefore has ______

A

vector / direction

57
Q

When a falling object loses GPE, it gains _____.
Therefore _____ lost = __________

A

gains KE
GPE lost = KE gained

58
Q

Power =

A

energy transfer / time

Physics (8 decks)

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