Forces and motion Flashcards

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1
Q

Acceleration eq

A

a = Δv/t Acceleration is negative acceleration (-)

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2
Q

What is Weight

A

The force acting on an object due to gravitational attraction

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3
Q

What is friction

A

The force which opposes the motion of an object Always in opposite direction to motion

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4
Q

Momentum eq

A

p = m x v
vector kg m/s

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5
Q

What is stopping distance

A

The total distance travelled during the time it takes for a car to stop in response to some emergency

It can be written as an equation involving two distances:
Stopping distance = Thinking distance + Braking distance

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6
Q

Principle of Moments

A

When an object is balanced, the total anticlockwise moment about a pivot = total clockwise moment about a pivot

Therefore you can use F 1 d 1 = F 2 d 2 If not it will turn

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7
Q

What happens when maverick opens his parachute?

A

There is a larger S.A so there is now more air resistance Reduces T.V

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8
Q

What is Terminal Velocity

A

The maximum speed that a moving object is able to reach Friction increases with speed ONLY till a certain point

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9
Q

Factors affecting breaking distance

A

How fast you are going, faster u r going, further distance
Mass of vehicles, larger mass, larger distance Quality of breaks Road surface/weather

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10
Q

What is the limit of proportionality (elastic limit)

A

When objects return to their original shape when the stretching force is removed

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11
Q

What is a moment

A

The turning effect of a force about a pivot

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12
Q

How to find COG

A

Suspend the shape and use a Plumb line from the same point Draw a line along it Do the same thing from different points COG is the centre of where lines point

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12
Q

When does the momentum of an object change

A

If it changes direction Its mass changes Accelerates or deccelerates

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13
Q

Resultant force eq

A

F = m x a

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14
Q

3 types of friction

A

Between solids - gripping Between solids sliding past each other Resistance/drag from fluids, e.g water or air

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15
Q

Speed, Velocity, Acceleration

A

Speed = D/t S = vt acceleration = (v-u)/at change in velocity/time v 2 =u 2 +2as

16
Q

What is acceleration

A

Rate of change of velocity (m/s 2 )

17
Q

Centre of Gravity

A

The point through which weight of a body acts A freely suspended object will swing until its COG is vertically below the point of suspension. You can calculate this with lines of Symmetry

18
Q

Supporting a beam

A

A light beam has no mass, therefore forces must be upwards (See book)

19
Q

Example of moment

A

the door handle is placed on the opposite side to the hinge
This means for a given force, the perpendicular distance from the pivot (the hinge) is larger
This creates a larger moment (turning effect) to make it easier to open the door
Opening a door with a handle close to the pivot would be much harder, and would require a lot more forceDoor handle is placed opposite to the hinge This means for x force the perpendicular distance from the hinge (pivot) is larger Therefore larger moment - Easier to open IF handle was near pivot it would be harder

20
Q

How do u calculate moment

A

M = F x d (Nm) d= perpendicular distance

21
Q

What are the safety measures in a vehicle

A

Crumple zone- Crumples increasing time to impact Seat belts - stretch increasing time taken Air bags - slow you down All of this reduces the force as time increases F = ([change] in momentum)/t

22
Q

Newtons 3rd law

A

Whenever two bodies interact the forces they exert on each other are equal and opposite When 2 objects collide (momentum) one will generally accelerate and one will deccelerate

23
Q

Newtons 2nd law

A

A resultant force means acceleration (f=ma)

24
Q

What is Newtons 1st law

A

As long as an object has 0 resultant force it was stay still or travel at a constant velocity (forces r balanced)

25
Q

Force and Change in Momentum Eq

A

F = (mv-mu)/t Force - change in momentum / time
Can be positive and negative

26
Q

Law of conservation of momentum

A

Momentum before = Momentum After

27
Q

What is inelastic deformation

A

When objects remain stretched and do not return completely to their original shape even when the stretching force is removed

Examples of materials that undergo inelastic deformation are:
Plastic
Clay
Glass

28
Q

What is Elastic Deformation

A

When objects return to their original shape when F is removed e.g. Rubber bands, Fabrics, Steel Springs

29
Q

What is Hooke’s law?

A

The extension of an elastic objec t is directly proportiona l to the force applied up to the limit of proportionality (elastic limit)

30
Q

Explain T.V in a skydiver [Maverick ejecting from F-14]

A

When he falls he has initially accelerates due to his weight, air resistance increases (upwards F) until it balances weight. As he speeds up, air resistance increases, now resultant F = 0 Therefore a = 0 and Terminal Velocity

31
Q

Factors affecting thinking distance

A

How fast driver is going Reaction time (drugs, alcohol, old age, tiredness)

32
Q

What is stopping distance made out of

A

Thinking Distance + Distance travelled in the time taken to react (m) Braking distance - Distance travelled once break has been pressed (m)

33
Q

Weight formula

A

W = m x g

34
Q

What is Weight

A

The force acting on an object due to gravitational attraction

35
Q

What is a vector quantity

A

Has magnitude and direction e.g. weight

36
Q

What is a scalar quantity

A

Only has magnitude e.g. mass

37
Q

What is a reaction force

A

The force between twow objects in contact Acts perpendicular to surface & away from it

38
Q

What is a force

A

Forces cause changes in: -Speed -Direction -Shape