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Physics > Forces > Flashcards

Forces Flashcards

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1
Q

Scalar

A

Magnitude only

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2
Q

Vector

A

Magnitude and direction

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3
Q

Examples of contact forces

A

Friction, air resistance, tension

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4
Q

Examples of non-contact forces

A

Gravitational force, electrostatic force and magnetic force

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5
Q

Weight

A

The force acting on an object due to gravity

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6
Q

How is weight measured

A

Newtonmeter

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7
Q

Why must more than one force be applied to compress, bend or stretch and object

A

Because if there was only one force acting in the object, it would accelerate in the direction of that force

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8
Q

Elastic deformation

A

When an object is deformed and returns back to its original shape once forces are removed

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9
Q

Inelastic deformation

A

When an object is deformed and doesn’t return to its original shape when forces are removed

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10
Q

Hooke’s Law

A

The extension of an elastic object, like a spring, is directly proportional to the force applied, provided that the limit of proportionality is not exceeded

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11
Q

Moment

A

Turning effect of a force

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12
Q

How does rotation occur

A

When forces are applied at a distance from the centre of mass

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13
Q

If an object is balanced..

A

The total clockwise moment = the total anticlockwise moment

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14
Q

Levers

A

Used to apple force to an object, by using a smaller force applied at one end of the lever to generate a larger force at the other end

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15
Q

Gears

A

Used to change the speed of direction of rotation

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16
Q

What happens to the density of the atmosphere with increasing altitude

A

The atmosphere becomes less dense

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17
Q

Explain why atmospheric pressure decreases with an increase in height

A
  • pressure is created by collisions of air molecules
  • the quantities of molecules (weight) decreases as the height increases
  • this means atmospheric pressure decreases with increased height
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18
Q

How does pressure in fluids increase with depth

A
  • As the depth increases, the mass of liquid above that depth also increases
  • This means that the force due to the mass increases
  • since the force has increased whilst the area remained constant, the pressure will increase
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19
Q

Why does pressure in fluids increase with density

A
  • as the density of a fluid increases, the number of particles in a given volume increases
  • so the weight of the fluid is greater
  • this means that the force from the fluid above a certain point is large
  • since the force has increased, so has the pressure
20
Q

Why are objects in a fluid subject to upthrust

A
  • when an object is submerged in a fluid, it has a higher pressure below it than it does above as there is more weight at the bottom than at the top
  • this leads to upthrust
21
Q

What is upthrust always equal to

A

The weight of fluid that the object displaces

22
Q

What factors influence whether an object will sink or float

A
  • upthrust
  • weight
  • density
23
Q

Explain why an object with a density greater than water can never float

A
  • upthrust is equal to the weight of the displaced fluid
  • if the density of the object is high, there wouldn’t be enough volume displaced to produce an upthrust larger than the objects weight
  • this means it will sink
24
Q

Atmosphere

A

A thin layer of air round the Earth

25
Q

Scalar quantities

A
  • mass
  • time
  • speed
  • volume
  • temperature
  • density
26
Q

Vector quantities

A
  • displacement
  • velocity
  • acceleration
  • momentum
  • force
  • weight
27
Q

Typical values for walking, running and cycling

A

Walking = ~1.5 m/s

Running = ~3 m/s

Cycling = ~6 m/s

28
Q

Velocity

A

Speed in a given direction

29
Q

Why does motion in a circle involve constant speed but changing velocity

A

Because velocity is a vector quantity that depends on speed and direction

30
Q

How to calculate speed of an object from a distance-time graph

A

The gradient

31
Q

Terminal velocity

A

The maximum speed of an object, reached when the forces moving the object are balanced by its frictional forces

32
Q

Explain what happens when a skydiver jumps out of a plane

A
  • initially the air resistance is small as the skydiver isn’t falling very quickly
  • as they speed up (accelerate), the air resistance increases, eventually growing large enough to balance the downwards weight force
  • once air resistance equals weight, the resultant force is 0
  • ## they’re not travelling at a constant speed (terminal velocity)
33
Q

Explain what happens when the skydiver opens a parachute

A
  • when the parachute opens there is a large upward force which causes the person to decelerate
  • eventually the forces balance again and the person reaches a new much slower terminal velocity
34
Q

Newton’s first law

A

If the resultant force acting on an object is 0 and:

  • the object is stationary, the object remains stationary
  • the object is moving, the object continues to move at a constant speed
35
Q

Inertia

A

The tendency of an object if at rest to continue in its state of rest, or if moving at a constant velocity to stay at a constant velocity

36
Q

Relationship between acceleration and inertial mass

A

Inversely proportional

Greater inertial mass = small acceleration
Smaller inertial mass = large acceleration

37
Q

Newtons Secind slaw

A

F=ma

38
Q

Newton’s third law

A

Whenever 2 objects interact, they exert equal and opposite force on each other

39
Q

Stopping distance

A

The sum of the distance the vehicle travels during drivers reaction time (thinking distance) and the distance it travels under the braking force (braking distance)

40
Q

What affects reaction time

A
  • tiredness
  • drugs
  • alcohol
  • distractions
41
Q

What affects braking distance

A
  • road and weather conditions (icy, wet)
  • condition of vehicle (brakes, tyres)
42
Q

Explain what happens to speed when brakes are applied

A

When a force is applied to the brakes of a vehicle, work done by the friction force of the brakes and wheels reduces the kinetic energy of the vehicle and temperature increases

43
Q

Relationship between braking and deceleration

A

The greater the breaking force the greater the deceleration

44
Q

Dangers of large decelerations

A

Brakes overheating or loss of control

45
Q

Momentum

A

Total momentum before an event = total momentum after the event

46
Q

Safety features of cars

A
  • air bags
  • seatbelts
  • crumple zones

Physics (10 decks)

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