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Physics > 5. Forces > Flashcards

5. Forces Flashcards

1
Q

What is a scalar quantity?

A

A quantity that only has a magnitude and isn’t direction dependent.

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2
Q

What is a vector quantity?

A

A quantity that has both a magnitude and an associated direction.

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3
Q

How can a vector quantity be drawn and what does it show?

A

As an arrow. The length of the arrow represents the magnitude, and the arrow points in the associated direction.

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4
Q

What is a force?

A

A push or pull acting on an object due to an interaction with another object.

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5
Q

What are the two categories that all forces can be split into?

A
  1. Contact forces (objects touching) 2. Non-contact forces (objects separated)
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6
Q

Give three examples of contact forces.

A
  1. Friction 2. Air resistance 3. Tension
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7
Q

Give three examples of non-contact forces.

A
  1. Gravitational forces 2. Electrostatic forces 3. Magnetic forces
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8
Q

Is force a vector or a scalar quantity?

A

Vector. It has both a magnitude and an associated direction.

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9
Q

Give three examples of vector quantities.

A
  1. Velocity 2. Displacement 3. Force
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10
Q

Give three examples of scalar quantities.

A

Temperature, Time, Mass, Speed, Distance, Energy.

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11
Q

What is weight?

A

The force that acts on an object due to gravity and the object’s mass.

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12
Q

What quantities does weight depend on?

A

Weight = mass x gravitational field strength. The object’s mass and the gravitational field strength at the given position in the field.

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13
Q

What is the unit used for weight?

A

The Newton (N).

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14
Q

What is the unit used for gravitational field strength?

A

N/kg.

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15
Q

What is meant by an object’s centre of mass?

A

The single point where an object’s weight can be considered to act through.

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16
Q

What piece of equipment can be used to measure an object’s weight?

A

A calibrated spring-balance or newton-meter.

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17
Q

What is the name given to the single force that is equivalent to all the other forces acting on a given object?

A

The resultant force.

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18
Q

What does it mean if a force is said to do ‘work’?

A

The force causes an object to be displaced through a distance.

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19
Q

What is the equation used to calculate work done? Give appropriate units.

A

Work done = Force x Distance. Work done (Joules), Force (Newtons), Distance (metres).

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20
Q

What distance must be used when calculating work done?

A

It must be the distance that is moved along the line of action of the force.

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21
Q

Under what circumstance is 1 joule of work done?

A

When a force of 1 Newton causes a displacement of 1 metre.

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22
Q

How many Newton-metres are equal to 1 joule of energy?

A

1 Nm = 1 J.

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23
Q

How much work is done by the force acting on the below object over a distance of 5m?

A

10 x 5 = 50 Nm = 50 J.

24
Q

What occurs when work is done against frictional forces?

A

A rise in temperature of the object occurs, and kinetic energy is converted to heat.

25
Q

Why does air resistance slow down a projectile?

A

The object does work against the air resistance, and kinetic energy is converted into heat, slowing down the object.

26
Q

Explain the relationship between the force applied and the extension of an elastic object.

A

The extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.

27
Q

What is meant by an inelastic deformation?

A

A deformation which results in the object being permanently stretched. The object doesn’t return to its original shape when the force is removed.

28
Q

State the equation relating force, spring constant and extension. Give appropriate units.

A

Force = Spring Constant x Extension. Force (N), Spring Constant (N/m), Extension (m).

29
Q

What type of energy is stored in a spring when it is stretched?

A

Elastic potential energy.

30
Q

What can extension be replaced with in the equation for spring force?

A

Compression.

31
Q

Does a distance quantity require a specific direction? i.e. is it a scalar or vector quantity?

A

No specific direction is required so it is a scalar quantity.

32
Q

If an object moves 3 metres to the left and then 3 metres back to its initial position, what is the object’s total displacement?

A

The object has zero displacement. Displacement is a vector quantity so it also involves direction. The object starts and ends at the same point.

33
Q

State a typical value for the speed of sound.

A

330 m/s.

34
Q

What is a typical value for human walking speed?

A

1.5 m/s.

35
Q

What is a typical value for human running speed?

A

3 m/s.

36
Q

What is a typical value for human cycling speed?

A

6 m/s.

37
Q

State the equation linking distance, speed and time. Give appropriate units.

A

Distance = Speed x Time. Distance (m), Speed (m/s), Time (s).

38
Q

How can speed be calculated from a distance-time graph?

A

The speed is equal to the gradient of the graph.

39
Q

State the equation for the average acceleration of an object. Give appropriate units.

A

Acceleration = (Change in Velocity)/(Time Taken). Acceleration (m/s²), Velocity (m/s), Time (s).

40
Q

Give an approximate value for the acceleration of an object in free fall under gravity near the Earth’s surface.

A

9.8 m/s².

41
Q

What can be said about the resultant force acting on an object when it is falling at terminal velocity?

A

The resultant force is zero. When at terminal velocity, the object is moving at a constant speed and so isn’t accelerating.

42
Q

State Newton’s first law for a stationary object.

A

If the resultant force on a stationary object is zero, the object will remain at rest.

43
Q

State Newton’s first law for a moving object.

A

If the resultant force on a moving object is zero, the object will remain at constant velocity (same speed in same direction).

44
Q

What can be said about the braking forces and driving forces when a car is travelling at constant velocity?

A

The braking forces are equal to the driving forces.

45
Q

If an object changes direction but remains at a constant speed, is there a resultant force?

A

Since there is a change in direction, there is a change in velocity and so there must be a resultant force.

46
Q

State the defining equation for Newton’s Second Law.

A

Resultant force = Mass x Acceleration. F = ma.

47
Q

State Newton’s Second Law in words.

A

An object’s acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass.

48
Q

What is the symbol used to represent an approximate value?

A

~.

49
Q

State Newton’s Third Law.

A

Whenever two objects interact, the forces that they exert on each other are always equal and opposite.

50
Q

What is the stopping distance of a vehicle equal to?

A

The sum of thinking distance and braking distance.

51
Q

For a given braking distance, if the vehicle’s speed is increased, what can be said about its stopping distance?

A

The stopping distance is increased with an increase in speed.

52
Q

Give a typical range of values for human reaction time.

A

0.2 seconds - 0.9 seconds.

53
Q

Give three factors which can affect a driver’s reaction time.

A
  1. Tiredness 2. Drugs 3. Alcohol
54
Q

Give two factors which may affect braking distance.

A
  1. Adverse (wet/icy) road conditions 2. Poor tyre/brake conditions.
55
Q

Describe the energy transfers that take place when a car applies its brakes.

A

Work is done by the friction force between the brakes and wheel. Kinetic energy of the wheel is converted to heat and is dissipated to the surroundings through the brake discs.

56
Q

To stop a car in a given distance, if its velocity is increased, what must happen to the braking force applied?

A

The braking force must also be increased.

57
Q

State two consequences of a vehicle undergoing very large decelerations.

A
  1. Kinetic energy converted to heat is very high causing brakes to overheat. 2. Loss of control of the vehicle.

Physics (7 decks)

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