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Physics - Lizzie > Forces And Motion > Flashcards

Flashcards in Forces And Motion Deck (30):
1

What is the equation for acceleration?

change in velocity ÷ time

2

What is the equation for average speed?

total distance ÷ total time

3

What is Newton's second Law?

force = mass x acceleration

4

How to work out moments

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

5

Principle of moments

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

6

Objects are more stable with:

• a lower centre of gravity
• a wider base

7

What is Hooke's Law?

• 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)

8

From where does weight act?

The centre of gravity of a Latina object.

9

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

• Vector quantities can have direction but scalar quantities don't.
• Both have magnitude.

10

What is the resultant force?

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).

11

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

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

12

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

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

13

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

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

14

When will an object reach terminal velocity?

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.

15

What is stopping distance?

The sum of the thinking distance and braking distance.

16

What factors affect thinking distance and reaction time?

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

17

What factors affect stopping distance?

• 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

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

0

19

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

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

20

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

• 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

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?

• 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

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?

• 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

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

• 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

Is density a scalar or vector quantity?

scalar

25

Is energy a scalar or vector quantity?

scalar

26

Is force a scalar or vector quantity?

vector

27

Is momentum a scalar or vector quantity?

vector

28

Is speed a scalar or vector quantity?

scalar

29

Is velocity a scalar or vector quantity?

vector

30

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

The distance moved is the area under the graph.