P10 Force and motion Flashcards

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1
Q

How to calculate the resultant force on an object from its acceleration and its mass

A

resultant force = mass x acceleration
resultant force (N), mass (kg), acceleration (m/s²)

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2
Q

Newton’s 2nd Law

A

States that the acceleration of an object is:
- proportional to the resultant force on the object
- inversely proportional to the mass of the object

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3
Q

Inertia

A

The tendency of an object to remain in its same state of uniform motion or rest

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4
Q

Inertial mass

A
  • A measure of how hard it is to change an object’s velocity.
  • It is defined as the ratio of force over acceleration.
  • Force / acceleration
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5
Q

When would the velocity of an object change?

A

If the velocity of an object changes, it must be acted on by a resultant force. Its acceleration is always in the same direction as the resultant force.

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6
Q

When would an object accelerate?

A
  • The velocity of the object increases (it accelerates) if the resultant force is in the same direction as the velocity
  • Its acceleration is positive because it is in the same direction as its velocity
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7
Q

When would an object decelerate?

A
  • The velocity of the object decreases (it decelerates) if the resultant force is in the opposite direction to its velocity
  • Its acceleration is negative because it is in the opposite direction to its velocity
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8
Q

How to calculate the force due to gravity

A

weight = mass x gravitational field strength
weight (N), mass (kg), gfs (N/kg)

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9
Q

What is the weight of an object?

A

The force acting on the object due to gravity

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10
Q

What is the mass of an object?

A

The quantity of matter in the object

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11
Q

What does the stopping distance of a vehicle depend on?

A

The thinking distance and the braking distance

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12
Q

How to calculate the stopping distance of a vehicle

A

stopping distance = thinking distance + braking distance

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13
Q

Thinking distance

A
  • The distance travelled by the vehicle in the time it takes the driver to react
  • Because the car moves at constant speed during the reaction time, the thinking distance is equal to the speed x reaction time
  • Thinking distance is proportional to the speed
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14
Q

Braking distance

A

The distance travelled by the vehicle during the time the braking force acts

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15
Q

Factors affecting stopping distances

A
  • Tiredness, alcohol, and drugs affect the brain and increase reaction times. Distractions like using a mobile phone also increase reaction time and cause serious accidents. All these factors increase the thinking distance, so the stopping distance is greater
  • The faster the vehicle is travelling, the further it travels before it stops. This is because the thinking distance and the braking distance both increase with increased speed
  • In adverse road conditions, for example on wet or icy roads, drivers have to brake with less force to avoid skidding. So stopping distances are greater in poor weather and road conditions
  • Poorly maintained vehicles, for example with worn brakes or tyres, take longer to stop because the brakes and tyres are less effective
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16
Q

What are the forces that oppose the driving force of a vehicle?

A

Friction and air resistance

17
Q

What does the braking force of a vehicle depend on?

A
  • The speed of the vehicle when the brakes are first applied
  • The mass of vehicle
18
Q

How to calculate momentum

A

momentum = mass x velocity
momentum (kg m/s), mass (kg), velocity (m/s)

19
Q

Law of conversation of momentum

A

States that in a closed system, the total momentum before an event is equal to the total momentum after the event

20
Q

Which equation links extension, force, and spring constant

A

force = extension x spring constant
force (N), extension (m), spring constant (N/m)

21
Q

What is meant when an object is called elastic?

A

An object is elastic if it returns to its original shape when the forces deforming it are removed

22
Q

How to measure the extension of an object when it is stretched

A

extension = length of the object - original length

23
Q

Hooke’s Law

A

The extension of a spring is directly proportional to the force applied, as long as its limit of proportionality is not exceeded

24
Q

Explain what is meant by ‘elastically deformed’

A

Will return to its original shape when the force is removed

25
Q

How do seatbelts reduce the force on people in car accidents?

A
  • Seatbelts are elastic and are designed to stretch a bit in a collision. This increases the time taken for the body’s momentum to reach zero, and so reduces the forces on it
  • The seatbelt acts across the chest, so it spreads the force out. Without the seatbelt, the force would act on the person’s head when it hit the windscreen
26
Q

How do airbags reduce the force on people in car accidents?

A
  • Air bags, in a car are designed to protect the driver and the front passenger. In a car crash, an inflated air bag spreads the force of an impact across the upper part of a person’s body.
  • It also increases impact time, increases the time taken for the head’s momentum to reach zero. So the effect of the force is lessened compared with just using a seatbelt
  • They also act as a soft cushion and percent cuts