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Physics - Lizzie > Forces And Motion > Flashcards

Forces And Motion Flashcards

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1
Q

What is the equation for acceleration?

A

change in velocity ÷ time

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2
Q

What is the equation for average speed?

A

total distance ÷ total time

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3
Q

What is Newton’s second Law?

A

force = mass x acceleration

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4
Q

How to work out moments

A

Moment = force x (perpendicular) distance from force to pivot

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5
Q

Principle of moments

A

For an object is equilibrium:
• total CM = total ACM
• total clockwise moment = total anti-clockwise moment

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6
Q

Objects are more stable with:

A
  • a lower centre of gravity

* a wider base

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7
Q

What is Hooke’s Law?

A
  • The idea stating that the extension of an elastic object is directly proportional to the force applied to it.
  • F = k x e
  • Force(N) = k(spring constant - N/m) x extension(m)
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8
Q

From where does weight act?

A

The centre of gravity of a Latina object.

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9
Q

What is the similarity and what is the difference between scalar and vector quantities?

A
  • Vector quantities can have direction but scalar quantities don’t.
  • Both have magnitude.
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10
Q

What is the resultant force?

A

The overall force acting in an object - an object with a resultant force of 0 will be going at a steady speed (or no speed).

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11
Q

What is Newton’s first law (balanced and unbalanced forces)?

A

• If the forces on an object are balanced, there is no change in velocity.

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12
Q

What is the equation to find the weight of an object?

A
  • weight = mass(kg) x acceleration due to gravity(m/s²)

* w = m x g

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13
Q

What would happen to objects if there were no air resistance as they fell?

A

They would all accelerate at the same speed (9.8m/s² - rounded to 10m/s²).

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14
Q

When will an object reach terminal velocity?

A

Once the resistance force on an object is equal to the accelerating force on an object, it can’t go any faster so it has reached its terminal velocity.

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15
Q

What is stopping distance?

A

The sum of the thinking distance and braking distance.

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16
Q

What factors affect thinking distance and reaction time?

A
  • Speed (even if reaction time doesn’t change, stopping distance increases).
  • Poor visibility (e.g. rain, fog).
  • Drugs/alcohol.
  • Fatigue.
17
Q

What factors affect stopping distance?

A
  • Speed.
  • Mass of the vehicle (bigger mass = longer stopping time).
  • How good the brakes are.
  • Grip on the road (affected by the road surface, weather conditions and the tyres).
18
Q

What is an object’s acceleration when it’s at terminal velocity?

A

0

19
Q

Why does a car’s speed decrease as it goes up a hill?

A

The car gains GPE whilst moving up the hill, which has to come from the kinetic energy of the car.

20
Q

Why does less work need to be done by the brakes if the car is on a hill?

A
  • Less work has to be done, as some of the car’s energy has been transferred to GPE.
  • There is a gravitational force which helps to slow the car down.
21
Q

Why would a journey involving lots of speeding up and slowing down use more petrol than a journey where the vehicle’s speed remains fairly constant?

A
  • More energy is used up when speeding up, as is more fuel burnt.
  • When stopping, kinetic energy is transferred to heat energy, which is lost in the atmosphere.
22
Q

When dropped at the same time, why would a feather reach the ground later than a hammer, although the feather has a greater force of air resistance?

A
  • The feather’s mass is much smaller than that of a hammer.
  • The feather will reach terminal velocity before the hammer because a smaller drag force is needed (drag=weight).
  • The feather therefore has a lower average velocity.
23
Q

Why is the acceleration of an aircraft accelerating down a runway not constant?

A
  • There is air resistance which increases as the velocity of the aircraft increases.
  • The air resistance then reduces the resultant force and the acceleration.
24
Q

Is density a scalar or vector quantity?

A

scalar

25
Q

Is energy a scalar or vector quantity?

A

scalar

26
Q

Is force a scalar or vector quantity?

A

vector

27
Q

Is momentum a scalar or vector quantity?

A

vector

28
Q

Is speed a scalar or vector quantity?

A

scalar

29
Q

Is velocity a scalar or vector quantity?

A

vector

30
Q

How can one deduce the distance which an object is done from looking at a velocity/time graph?

A

The distance moved is the area under the graph.

Physics - Lizzie (19 decks)

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