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Physics > Module 3 - Forces/Motion - Defintions > Flashcards

Module 3 - Forces/Motion - Defintions Flashcards

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1
Q

Acceleration

A

The rate of change of velocity.

Found from the gradient of a velocity-time graph

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2
Q

Archimede’s Principle

A

The upwards force (upthrust) acting on an object submerged in a fluid is equal to the weight of the fluid it displaces.

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3
Q

Average Speed

A

Distance over time for the entire region of interest

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4
Q

Braking Distance

A

The distance travelled between the brakes being applied and the vehicle coming to a stop.

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5
Q

Brittle

A

A material which shows no plastic deformation before reaching its breaking stress.

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6
Q

Centre of Gravity

A

The single point through which the object’s weight can be said to act.

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7
Q

Centre of Mass

A

The single point through which the object’s mass can be said to act.

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8
Q

Compression

A

The result of two coplanar forces acting into an object. Compression usually results in a reduction in the length of the object.

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9
Q

Compressive Deformation

A

The changing of an object’s shape due to compressive (pushing or squashing) forces.

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10
Q

Conservation of Energy

A

In a closed system with no external forces the total energy of the system before an event is equal to the total energy of the system after the event. The energy does not need to be in the same form after the event as it was before the event.

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11
Q

Conservation of Momentum

A

The total momentum of a system before an event must be equal to the total mometnum of the system after the event, assuming no external forces act. Total momentum is found by the vector addition of the individual momentums of all parts of the system.

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12
Q

Couple

A

Two equal sized anti-parallel forces that act on an object through different lines of action.

It has the effect of turning without translation (changing the position of the object).

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13
Q

Density

A

The mass per unit volume of a material.

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14
Q

Displacement

A

The direct distance between an object’s starting and ending positions.

It is a vector quantity, and so has both a direction and magnitude.

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15
Q

Displacement - Time graphs

A

Plots showing how displacement changes over a period of time.

The gradient gives the velocity. Curved lines represent an acceleration.

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16
Q

Drag

A

The frictional force than an object experiences when moving through a fluid.

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17
Q

Ductile

A

A material is ductile if it can undergo very large amounts of plastic deformation under tension.

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18
Q

Efficiency

A

The useful output (e.g. power, energy) of a system divided by the total output.

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19
Q

Elastic Collisions

A

A collision where the total kinetic energy of the system before the collision is equal to the total kinetic energy of the system after the collision.

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20
Q

Elastic Deformation

A

It a material deforms with elastic behaviour, it will return to its original shape when the deforming forces are removed. The object will not be permanently deformed.

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21
Q

Elastic Hysteresis

A

A property of polymers such as rubber. This is when the work done to on loading a rubber band is greater than the energy returned when the rubber band is unloaded. This means the loading line sits above the unloading line on a force-extension graph.

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22
Q

Elastic Potential Energy

A

The energy stored in an object when it is stretched or compressed. It is equal to the work done to stretch/compress the object and can be determined from the area under a force-extension graph.

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23
Q

Equilibrium

A

For an object to be in equilibrium, the resultant force and the resultant moment acting on the object must be equal to zero.

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24
Q

Extension

A

The increase in an object’s length

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25
Q

Force-Extension Graph

A

A plot showing how an object extends as teh force applied increases. For an elastic object following Hooke’s law, the gradient should be linear up to the limit of proportionality. The gradient gives the stiffness constant or spring constant.

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26
Q

Free-Body Diagram

A

A diagram showing all the forces acting on an object.

It is a good starting point to any mechanics problem.

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27
Q

Freefall

A

An object is said to be in freefall when the only force acting on it is the force of gravity.

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28
Q

Friction

A

The resistive force produced when there is relative movement between two surfaces.

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29
Q

Gravitational Potential Energy

A

The energy gained by an object when it is raised by a height in a gravitational field.

30
Q

Hooke’s Law

A

The extension of an elastic object will be directly proportional to the force applied to it, up to the limit of proportionality.

31
Q

Impulse

A

The change in momentum of an object when a force acts on it. It is equal to the product of the force acting on the object and the length of time over which it acts, and can be found from the area under a force-time graph.

32
Q

Inelastic Collisions

A

A collision where the total kinetic energy of the system before the collision is not equal to the total kinetic energy of the system after the collision.

33
Q

Instantaneous speed

A

The exact speed of an object at a specific given point.

34
Q

Kinetic Energy

A

The energy an object has due to its motion. It is the amount of energy that would be transferred from the object when it decelerates to rest.

35
Q

Linear Momentum

A

The product of an object’s mass and linear velocity. Momentum is a vector quantity.

36
Q

Moment of Force

A

The product of a force and the perpendicular distance from the line of action of the force to the pivot.

37
Q

Newton

A

The unit of Force.

38
Q

Newton’s First Law

A

An object will maintain constant velocity, unless acted on by a resultant force.

39
Q

Newton’s Second Law

A

The resultant force acting on an object is equal to the rate of change of momentum of the object.

It is also expressed as the resultant force acting on an object is equal to the product of the object’s mass and acceleration.

40
Q

Newton’s Third Law

A

If body A exerts a force on body B, then body B exerts the same magnitude force on body A in the opposite direction.

41
Q

Newton’s Third Law pairs of Forces

A

Must be the same magnitude, same type of force, acting along the same line of action. They act in opposite directions and on two different objects (body A and body B).

42
Q

Normal Contact Force

A

The reaction force between an object and a surface.

43
Q

Pivot

A

The point about which a body can rotate is a moment acts on it.

44
Q

Plastic Deformation

A

If a material deforms with plastic behaviour, it will not return to its original shape when the deforming forces are removed. The object will be permanently deformed.

45
Q

Polymeric

A

A material made from polymers (long chained molecules)

46
Q

Power

A

The rate at which work is done (or energy transferred) by a system.

47
Q

Pressure

A

The force that a surface experiences per unit area. It is measured in Pascals (Pa)

48
Q

Principle of Moments

A

For an object to be in equilibrium, the sum of the clockwise moments acting about any point must be equal to the sum of the anticlockwise moments acting about the point.

49
Q

Projectile Motion

A

The motion of an object that is fired from a point and then upon which only gravity acts.

When solving projectile motion problems, it is useful to split the motion into horizontal and vertical components.

50
Q

Reaction Time

A

The time taken to process a stimulus and trigger a response to it.

It is affected by alcohol, drugs and tiredness.

51
Q

Resultant force

A

The total force acting on an object, found by the vector addition of each of the separate forces that act on the object.

52
Q

Speed

A

The rate of change of distance.

53
Q

Spring Constant

A

The constant of proportionality for the extension of a spring under a force. The value of the Spring Constant tells you how many Newtons of force are required to obtain a metre of extension. The higher the number, the more stiff the sample, and the steeper the gradient of the force-extension graph.

54
Q

Stiffness

A

The ability of a material to resist deformation.

55
Q

Stiffness Constant

A

Another term for the Spring Constant.

56
Q

Stopping Distance

A

The sum of the thinking distance and braking distance for a driven vehicle.

57
Q

Strain

A

The ratio of an objects extension to its original length. It is a ratio of two lengths, and so has no unit (although it can be stated as a percentage - be careful of this when doing calculations involving strain).

58
Q

Stress

A

The amount of force acting per unit cross-sectional area. Its unit is the Pascal (Pa).

59
Q

Tensile Deformation

A

The changing of an object’s shape due to compressive forces.

60
Q

Tension

A

The resultant of two forces acting on an object in opposite, outwards directions.

61
Q

Terminal Velocity

A

The maximum velocity of an object that occurs when the resistive and driving forces acting on the object are equal to each other.

62
Q

Thinking Distance

A

The distance travelled during the drivers reaction time.

It found by multplying the vehicle’s speed and the reaction time of the driver.

It is affected by alcohol, drugs, tiredness, and distractions.

63
Q

Triangle of Forces

A

A method of finding the resultant force of two forces.

The two forces are joined tip to tail and the result is then the vector that completes the triangle.

64
Q

Upthrust

A

The upwards force that a fluid applies on an object. The size of the upthrust force can be found by applying Archimede’s principle.

65
Q

Ultimate Tensile Strength

A

The maximum stress that an object can withstand before fracture occurs.

66
Q

Velocity

A

The rate of change of displacement. It is a vector quantity and so has both a direction and a magnitude.

67
Q

Velocity-Time Graphs

A

Plots showing how velocity changes over a period of time. The gradient gives acceleration. Curved lines represent changing acceleration.

68
Q

Weight

A

The product of an object’s mass and the gravitational field strength at its location.

69
Q

Work done

A

The energy transferred when a force moves an object over a distance. It is found by the product of the distance moved and the component of the force parallel to the direction of movement.

70
Q

Yield Point

A

A point on a stress-strain graph beyond which the deformation is no longer entirely elastic.

71
Q

Young Modulus

A

The ratio of stress to strain for a given material. Its unit is the Pascal (Pa). The Young Modulus is a material property, whereas the Spring Constant is specific to a single sample. The vaule for the Young Modulus represents the force required to extend a metre cubed block of a material by one metre, so it is often a very large number.

Physics (9 decks)

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