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PHYSICS > 0.4 Mechanics > Flashcards

0.4 Mechanics Flashcards

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1
Q

What is a scalar?

A

A quantity that only has amount (magnitude).

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2
Q

What is a vector?

A

A quantity with both direction and magnitude.

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3
Q

Name 6 scalars.

A

1) Time
2) Mass
3) Temperature
4) Length
5) Speed
6) Energy

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4
Q

Name 6 vectors.

A

1) Weight
2) Acceleration
3) Force
4) Displacement
5) Velocity
6) Momentum

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5
Q

What are two different ways to combine vectors?

A
  • Drawing scale diagrams
  • Using pythagoras and triganometry
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6
Q

When answering questions about vectors, if the vector given uses directions of a compass, then you should what?

A

Then your answer must be given as a bearing.

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7
Q

How do you show forces acting on an object?

A

Drawing a free body diagram.

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8
Q

What does it mean for an object to be in equilibrium?

A

When all forces acting on the object are balanced and cancel each other out.
- This also includes rotational forces (moments)
- The resultant force will therefore be 0 aswell as acceleration.

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9
Q

What is the official definition of 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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10
Q

What is the equation for a moment?

A

M = F x d
Moment = force x perpendicular distance from pivot to the line of action of force

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11
Q

What is the Principle of moment?

A

If a system is in equilibrium,
the sum of the clockwise moments = the sum of the anticlockwise moments

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12
Q

What is a couple?

A

A pair of forces that are equal in size and act parallel to each other but in opposite direction.

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13
Q

What is the centre of mass?

A

The single point where all the weight is considered to act through.

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14
Q

What does uniform mean?

A

The density of the material is the same throughout, resulting in the centre of mass always being in the middle.

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15
Q

What is the definition of displacement?

A

Distance and direction from the starting point in a straight line.

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16
Q

What is the definition of speed?

A

How fast something is going regardless of direction.

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17
Q

What is the definition of velocity?

A

How fast something is going with direction.

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18
Q

What is the definition of acceleration?

A

The rate of change of velocity.

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19
Q

If a object is not accelerating, what formulae can we use?

A

Speed = Distance / Time

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20
Q

However if an object is accelerating, what equations can we use?

A

SUVAT equations

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21
Q

What does the gradient of a displacement time graph represent?

A

Velocity

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22
Q

What does a curved line represent in a displacement time graph?

A

Changing velocity / acceleration

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23
Q

What does the gradient of a velocity time graph represent?

A

Acceleration

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24
Q

What does the area under the line represent in a velocity time graph?

A

Displacement

25
Q

What are the two methods to work out the area under the graph?

A

1) Divide up into triangles and rectangles (for a straight line)
2) Count the squares (use for curved lines)

26
Q

What does a curved line on a velocity time graph show?

A

A change of acceleration

27
Q

What does the area under the line of an acceleration time graph represent?

A

Change in velocity

28
Q

What does Newtons 1st Law state?

A

If there are no resultant forces acting on an object it will either:
1) Stay at rest
2) Travel at a constant speed in a straight line

29
Q

What does Newtons 2nd Law state?

A

The acceleration of an object is proportional to the resultant force acting on it: F = m x a
- Where there is an acceleration ther must be a force
- Where there is a force there is an accereleration

30
Q

What does Newtons 3rd Law state?

A

If object A exerts a force on object B, then object B exercts an equal but opposite force on object A

31
Q

What are the rules for Newtons 3rd Law?

A

1) Two objects involved
2) Same type of force
3) Same size but in opposite directions

32
Q

What does freefall mean?

A

When an object is in freeall the only force acting on that object is its weight.

33
Q

What is air resistance proportional to?

A

Surface area and speed

34
Q

Why when there is no acceleration do all objects accelerate at the same rate?

A

Because acceleration is independent of mass.

35
Q

How did Galileo record freefall ‘accurately’?

A

He rolled balls with different masses down a slope.

  • Acceleration is still caused by gravity but rolled slower, making it easier to time and for air resistance to be negligible.
  • He timed how long it took the balls to roll down different lengths of the slope and found the distance travelled was always the same.
36
Q

What is a projectile?

A

An object where the only force acting on it is it’s weight, therefore it is in freefall.

37
Q

Is there a horizontal force acting on a projectile?

A

No, as we are assuming that air resistance is negligible.

38
Q

If there is no horizontal force acting on a projectile, then what happens to the horizontal velocity?

A

It will stay constant.

39
Q

How do you calculate the horizontal component (projectiles)?

A

Horizontal component = horizontal velocity x time in air

40
Q

Why will the projectile accelerate in the vertical direction?

A

Because the vertical force of weight is acting on it, and acceleration is typically due to g=9.81m/s^2

41
Q

If the projectile is fired horizontally then what is the vertical speed be?

A

Speed will be 0

42
Q

For every second a projectile is in flight how much velocity will be gained?

A

9.81 ms^-1

43
Q

Is the vertical and horizontal components of motion related?

A

No they are completely independent.

44
Q

What difference will air resistance will air resistance make to a projectiles path if it is no negligible?

A
  • The horizontal velocity will slowly decrease to 0 as a horizontal force is now acting.
  • It will therefore not travel as far horizontally.
  • The projectile will gain vertical speed more slowly.
45
Q

What is the simple definition on for friction?

A
  • It is a force that opposes motion
  • It turns kinetic energy into thermal energy
  • It can never speed things up or start them moving.
46
Q

What are the two types of friction?

A

1) contact friction
2) fluid friction

47
Q

What is contact friction?

A

Friction between two solid surfaces.

48
Q

What is fluid friciton?

A

Better known as drag, which is caused by a gas or a liquid.

49
Q

What does drag increase with?

A
  • Larger surface area (of the projectile)
  • Larger speed (proportional to speed squared)
  • Larger density (viscosity) of fluid
  • Nothing to do with mass
50
Q

What is lift?

A

Lift is 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.

51
Q

What direction does lift act?

A

Perpendicular to the direction of fluid flow (relative to the object)

52
Q

What direction does drag act?

A

Drag acts parallel to the direction of the fluid flow.

53
Q

What is terminal velocity?

A

The maximum speed of an object that occurs when the resistive and driving forces acting on the object are equal to each other.

54
Q

What is linear momentum?

A

The product of an objects mass and velocity.
It is a vector quantitiy.

55
Q

What is the equation of momentum?

A

Momenmtum = mass x velocity

56
Q

What does the principle of (conservation of) linear momnetum state?

A

The momentum before collision = total momentum after collision, provided no external forces act.

57
Q

What does inelastic collision mean?

A
  • Momentum conserved
  • Kinetic energy NOT conserved
  • Most collisions in real life are inelastic
  • Energy is lost as heat and sound
58
Q

What does elastic collisions mean?

A
  • Momentum conserved
  • Kinetic energy conserved
59
Q

What happens in an elastic collision between two objects of the same mass?

A

PHYSICS (8 decks)

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