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Physics > Forces And Motion > Flashcards

Forces And Motion Flashcards

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1
Q

What is the equation for average speed ?

A

Distance moved / time taken

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2
Q

What is the difference between speed and velocity

A
  • Speed is how fast your going

* Velocity must also have the direction specified

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3
Q

What is the equation for acceleration ?

A

Change is velocity / time taken

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4
Q

What is acceleration?

A
  • How quickly the velocity is changing

* Change in velocity can be a change in SPEED or DIRECTION or both

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5
Q

What is the weight equation ?

A

Mass x gravitational field strength

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6
Q

What are the different types of forces ?

A
  • Gravity or weight
  • Reaction force
  • Electrostatic force
  • Thrust (e.g. push and pull)
  • Drag or Air resistance or Friction (slowing thing down)
  • Lift (e.g. aeroplane wing)
  • Tension (e.g. rope or cable)
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7
Q

What is Friction and Why is it there?

A
  • Force that opposes motion

* There to slow things down

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8
Q

How does Friction occur?

A
  • Between solid surfaces which are gripping
  • Between solid surfaces which are sliding past each other
  • Resistance/drag from fluids
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9
Q

How can you Reduce Friction between Solid Surfaces?

A

Put lubricant (oil/grease) between surfaces

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10
Q

How can Investigate the Motion of the Toy Car on a ramp?

A
  • Set up ramp with car on top
  • Measure distance between light gate (to find car average speed)
  • When car goes through light gate, light broken, time recorded by data logging
  • Repeat x10, get average time for car to reach light gate
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11
Q

What is the First Law?

A

Balanced forces mean no change in velocity

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12
Q

What is the Second Law?

A

A resultant force means acceleration

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13
Q

What forms can Acceleration be in?

A
  • Starting
  • Stopping
  • Speeding up
  • Slowing down
  • Changing direction
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14
Q

Force=

A

Mass x Acceleration

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15
Q

What is the Third law?

A

If object A exerts a force on object B then object B exerts an equal and opposite force an object A

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16
Q

What are Examples of Vectors Quantities?

A
  • Force
  • Velocity
  • Acceleration
  • Momentum
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17
Q

What are Examples of Scalar Quantities?

A
  • Mass
  • Temperature
  • Time
  • Length
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18
Q

What are Vector Quantities?

A

Have size and direction

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19
Q

What are Scalar Quantities?

A

Have size and no direction

20
Q

How can Objects reach a Terminal Velocity?

A
  • First fall - more force accelerating it than resistance slowing it down
  • Velocity Increases - resistance builds up
  • Resistance reduces acceleration until resistance force equal to acceleration force
  • Reached terminal velocity
21
Q

What is Gravity?

A

Accelerating force acting on all falling objects

22
Q

What does the Terminal Velocity of Falling Objects depend on?

A
  • Determined by drag compared to weight

* Drag depends on its shape & area

23
Q

What is an example using a Human Skydiver to explain why Terminal Velocity of Falling Objects is Dependant on their Shape and Area:

A
  • No parachute - small area, force equal to weight pulling him down
  • Terminal velocity - 120mph
  • Parachute - more air resistance, same force pulling him down
  • Terminal velocity - 15mph
24
Q

What is Hooke’s Law?

A

Extension proportional to force

25
Q

How can you Investigate Hooke’s Law with a Spring?

A
  • Weighing stand, spring with hanging mass attached
  • Measure length of spring
  • Add one mass at a time, measure new length
  • Extension - change in length from original length
  • Repeat process x10
  • Increase in mass = Increase In extension
26
Q

How can Hooke’s Law Stop Working?

A
  • Force great enough
  • Force past elastic limit, material permanently stretched
  • Force removed, material longer than at start
27
Q

Stopping Distance =

A

Thinking Distance + Braking Distance

28
Q

What Affects Thinking Distance?

A
  • How fast your going

* Reaction time (drugs, tiredness, alcohol, inexperienced)

29
Q

What Affects Braking Distance?

A
  • How fast your going
  • Mass of vehicle (larger mass-longer takes to stop)
  • Quality of brakes
  • Quality of grip - depends on road surface, weather, tyres
30
Q

Momentum (kgm/s)=

A

Mass(Kg) x Velocity (m/s)

31
Q

Momentum Before =

A

Momentum After

32
Q

What happens when a Force acts on a object?

A
  • Causes change in momentum

* Larger force = faster change

33
Q

Force (N) =

A

Change in momentum (kgm/s) / time(s)

34
Q

How do Crumple Zones Reduce an Accident?

A
  • Crumple on impact

* Increasing time taken for car to stop

35
Q

How do Seat Belts Reduce an Accident?

A
  • Stretch slightly
  • Increasing time taken for wearer to stop
  • Reduces forces acting on chest
36
Q

How do Air Bags Reduce an Accident?

A

Slows you down more gradually

37
Q

Moment (Nm) =

A

Force (N) x perpendicular distance (m) between line of action and pivot

38
Q

What is a Moment?

A

Turning effect of a force

39
Q

How to get a Maximum Moment on Spanner?

A

Push at right angles (perpendicular) to spanner

40
Q

How do you get a Larger Moment on a Spanner?

A
  • Larger force

* Longer spanner - distance from pivot is greater

41
Q

What is the Centre of Gravity?

A
  • Point through which weight of a body acts

* Object swing until centre of gravity vertically below point of suspension

42
Q

How can you find the Centre of Gravity of a Flat Shape?

A
  • Suspend shape & plumb line at same point,wait until not moving
  • Draw line along plumb line
  • Do same thing again, but suspend shape from different pivot point
  • Centre is Gravity = 2 lines cross
43
Q

What does the Principle of Moments say?

A

If an object is balanced then : Total anticlockwise moments = total clockwise moments

44
Q

Why are Forces Not always Equal across all supports?

A
  • Light rod - supported at both ends, upwards force by each support won’t always be same
  • Heavy object - placed on rod, support closest to object will provide larger force
45
Q

What does it mean if Moments are Not Equal?

A

There will be a resultant moment - object turn

Physics (7 decks)

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