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