Flashcards in GCSE Physics- Crucial Definitions Deck (23)

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1

## Vector quantity

### A quantity which is defined by three things, a magnitude, a direction and a unit

2

## Scalar quantity

### A quantity which is defined by two things, Magnitude and unit.

3

## State Newtons 1st law.

###
The forces on a system are balanced therefore Fr=0, the object will not accelerate.

The object has two possible states of motion;

•Stationary

•Moving at a constant velocity.

4

## State Newtons 2nd law.

### Fr=m a, and so Fr/m=a; the acceleration, a of a body is directly proportional to the resultant force,Fr, and inversely proportional to the mass, m

5

## What is mass

### Is a measure for the amount of matter of an object

6

## What is weight

### Is the size of the gravitational force of an object

7

## What is density

### Density is the mass per unit volume d=m/V

8

## State Hooke's Law

### The extension of a spring is directly proportional to the applied force up to the limit of proportionality

9

## What is pressure

### The force per unit area

10

## What is conservation of energy?

### Energy cannot be created or destroyed, merely transferred from one to the other.

11

## What is efficiency

### Efficiency is the ratio of useful energy out/total energy in. It is a measure of effectiveness of a device at transferring energy into a desired form.

12

## What is power?

### Power is the rate of doing work or the rate if transferring energy.

13

## What is a moment?

### A moment is the product of force (F) multiplied by the perpendicular distance (d).

14

## State the principle of moments.

### For a system in rotational equilibrium the sum of the clockwise moments=Sum of anti-clockwise moments about any point (or the pivot point).

15

## What is the centre of mass?

### The point which through the entire mass of the object appears to be concentrated.

16

## What is the centre of gravity?

### The point through which the entire weight of an object appears to act.

17

## What is an Atomic mass number?

### The number of protons and neutrons in an atom.

18

## What is an atomic number

### The number of protons in an atom.

19

## What is ionisation?

### The process by which an atom or molecule acquires a negative or positive charge by losing or gaining electrons or form ions.

20

## What is an isotope

### Variants of the same element with the same number of protons but different number of neutrons.

21

## What is a half life?

### The average time taken for the number of radioactive nuclei to reach half its initial value,or the average time taken for the activity of a radioactive source to reach half its initial value.

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## What is activity of a source?

### The number of disintegrations per second of a source.

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