# Physics Glossary

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- Created by: Abu2002
- Created on: 05-01-19 14:08

Acceleration

Change of velocity per unit time

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Acceleration of free fall

Acceleration of an object acted on only by the force of gravity

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Accurate

A measurement that is obtained, using accurately-calibrated instruments correctly, is said to be accurate

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Accuracy

A measurement is considered accurate if it is judged to be close to the true value

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Base units

The units that define the SI system (e.g., the metre, the kilogram, the second, the ampere)

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Breaking distance

The distance travelled by a vehicle in the time taken to stop it

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Centre of mass

The centre of mass of a body is the point through which a single force on the body has no turning effect

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Couple

Pair of equal and opposite forces acting on a body but not along the same line

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Density of substance

Mass per unit volume of the substance

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Displacement

Distance in a given direction

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Drag force

The force of fluid resistance on an object moving through the fluid

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Effort

The force applied to a machine to make it move

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Elastic limit

Point beyond which a wire is permanently stretched

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Elasticity

Property of a solid that enables it to regain its shape after it has been deformed or distorted

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Energy

The capacity to do work

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Equilibrium

State of an object when at rest or in uniform motion

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Error bar

Representation of an uncertainty on a graph

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Error of measurement

Difference between a measured value and the true value. Errors can include systematic (including zero error) and random

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Force

Any interaction that can change the velocity of an object

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Free body diagram

A diagram of an object showing only the forces acting on the object

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Friction

Force opposing the motion of a surface that moves or tries to move across another surface

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Gravitational field force

Force of gravity per unit mass on a small object

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Hooke's law

The extension of a spring is proportional to the force needed to extend it

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Inertia

Resistance of an object to change of its motion

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Kinetic energy

The energy of an object due to its motion

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Limit of proportionality

The limit beyond which, when a wire or a spring is stretched, its extension is no longer proportional to the force that stretches it

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Linear

Two quantities are said to have a linear relationship if the change of one quantity is proportional to the change of the other

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Load

The force to be overcome by a machine when it shifts or raises an object

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Mass

Measure of the inertia or resistance to change of motion of an object

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Moment of force about point

Force × perpendicular distance from the line of action of the force to the point

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Momentum

mass × velocity

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Newtons First

An object remains at rest or in uniform motion unless acted on by a resultant force

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Newtons Second

The rate of change of momentum of an object is proportional to the resultant force (F) on it. Newton’s 2nd law may be written as F = (Δmv)/Δt. For constant mass, this equation becomes F = ma where acceleration a = (Δv/Δt)

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Pascal

Unit of pressure or stress equal to 1 N m –2

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Potential difference

Work done or energy transfer per unit charge between two points when charge moves from one point to the other

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Potential energy

The energy of an object due to its position

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Power

Rate of transfer of energy

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Precision of a measurement

Precise measurements are ones in which there is very little spread about the mean value. Precision depends only on the extent of random error and it gives no indication of how close the results are to the true value

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Precision of a instrument

The smallest non-zero reading that can be measured, also sometimes referred to as the instrument sensitivity or resolution

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Pressure

Force per unit area acting on a surface perpendicular to the surface

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Principle for the conservation of energy

Energy cannot be created or destroyed

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Principle of moments

For an object in equilibrium, the sum of the clockwise moments about any point = the sum of the anticlockwise moments about that point

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Probable error

Estimate of the uncertainty of a measurement

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Projectile

A projected object in motion acted on only by the force of gravity

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Random error

Error of measurement due to results varying in an unpredictable way from one measurement to the next. They cannot be corrected. The effect of random errors can be reduced by making more measurements and calculating a new mean

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Range of a set of readings

The range of a set of readings of the same measurement is the difference between the minimum and the maximum reading

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Range of an instrument

The difference between the minimum and the maximum reading that can be obtained using the instrument

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Scalar

A physical quantity with magnitude only

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Sensitivity of an instrument

The output reading per unit input quantity

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SI system

The scientific system of units

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Speed

Change of distance per unit time

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Stopping distance

thinking distance + braking distance

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Systematic error

Cause readings to differ from the true value by a consistent amount each time a measurement is made. Sources of systematic errors can include the environment, methods of observation, or instruments used

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Terminal speed

The maximum speed reached by an object when the drag force on it is equal and opposite to the force causing the motion of the object

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Thinking distance

The distance travelled by a vehicle in the time it takes the driver to react

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Uncertainty

The interval within which the true value can be expected to lie, with a given level of confidence or probability

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Useful energy

Energy transferred to where it is wanted when it is wanted

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Vector

A physical quantity with magnitude and direction

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Velocity

Change of displacement per unit time

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Weight

The force of gravity acting on an object

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Work

force × distance moved in the direction of the force

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Zero Error

Any indication that a measuring system gives a false reading when the true value of a measured quantity is zero. A zero error may result in a systematic uncertainty

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## Other cards in this set

### Card 2

#### Front

Acceleration of an object acted on only by the force of gravity

#### Back

Acceleration of free fall

### Card 3

#### Front

A measurement that is obtained, using accurately-calibrated instruments correctly, is said to be accurate

#### Back

### Card 4

#### Front

A measurement is considered accurate if it is judged to be close to the true value

#### Back

### Card 5

#### Front

The units that define the SI system (e.g., the metre, the kilogram, the second, the ampere)

#### Back

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