GCSE Physics: Forces and Newton's Laws Flashcards

Question 1

Define Scalar Quantity.

Accepted Answer

A quantity described fully by a size alone, with no direction attached, so two of them are combined by ordinary arithmetic rather than by drawing arrows on a diagram.

Question 2

Define Vector Quantity.

Accepted Answer

A quantity that is only fully described once a direction is given as well as a size. It is drawn as an arrow whose length represents the size and whose head shows the direction.

Question 3

Define Contact Force.

Accepted Answer

A force that can only act while two objects are physically touching each other, disappearing the instant they separate.

Question 4

Define Non-Contact Force.

Accepted Answer

A force acting between two objects that are separated, carried across the gap by a field rather than by anything touching.

Question 5

What is Newton?

Accepted Answer

The SI unit in which every force is measured, given the symbol N. Arrows on a free-body diagram are labelled in newtons, and a medium apple held in your hand pushes down with roughly one.

Question 6

What is Mass?

Accepted Answer

A scalar measure of how much matter an object contains, recorded in kilograms. Moving the object to another planet or into orbit does not alter it.

Question 7

What is Weight?

Accepted Answer

The downward force a gravitational field exerts on an object, recorded in newtons and treated as acting at a single point called the centre of mass. It is measured with a calibrated newtonmeter.

Question 8

Define Gravitational Field Strength.

Accepted Answer

The pull of gravity on each kilogram of matter at a given place, symbol g, quoted in newtons per kilogram. Multiplying it by an object's mass gives that object's weight.

Question 9

Define Free-Body Diagram.

Accepted Answer

A sketch showing one chosen object as a dot or a box, with every force acting on it drawn as a labelled arrow and nothing else included on the page.

Question 10

Define Resultant Force.

Accepted Answer

The one force that could replace every force acting on an object and produce exactly the same motion. Forces pointing the same way add together, while opposing forces subtract.

Question 11

What is Equilibrium?

Accepted Answer

The condition in which the forces on an object cancel out completely, so its velocity cannot change. Drawn to scale, the force arrows join head to tail to form a closed shape.

Question 12

Define Newton's First Law.

Accepted Answer

The rule that velocity changes only when a resultant force acts. Everyday objects appear to slow down because friction and drag supply such a force, not because motion itself needs a push to continue.

Question 13

What is Inertia?

Accepted Answer

The property that makes any change of velocity demand a force. Passengers lurch forwards as a bus brakes because nothing has yet acted on them to slow them down.

Question 14

Define Newton's Second Law.

Accepted Answer

The rule that acceleration rises in proportion to the resultant force and falls in proportion to mass, written F = ma with newtons, kilograms and metres per second squared.

Question 15

Define Inertial Mass.

Accepted Answer

A measure of how hard it is to change an object's velocity, defined as the ratio of the resultant force applied to the acceleration that force produces.

Question 16

Define Newton's Third Law.

Accepted Answer

The rule that forces always come in pairs: if A pushes B, then B pushes A just as hard the opposite way. The pair are always the same type and act on different objects.

Question 17

Define Normal Contact Force.

Accepted Answer

The push a surface gives an object resting against it, directed at right angles to that surface. Its size adjusts itself to whatever keeps the object from sinking in.

Question 18

What is Friction?

Accepted Answer

A contact force between two surfaces that resists them sliding past one another, warming both as it transfers energy to the thermal store of the surroundings.

Question 19

What is Drag?

Accepted Answer

The resistive force on an object travelling through a fluid such as air or water. It points against the direction of travel and grows larger the faster the object moves.

Question 20

Define Terminal Velocity.

Accepted Answer

The steady speed at which an object stops accelerating through a fluid, reached once the resistive force has grown until nothing is left over to change the velocity.

Question 21

Define Work Done.

Accepted Answer

The energy transferred when a force shifts its point of application along the line in which it acts, found by multiplying force by distance moved and recorded in joules.

Question 22

Define Hooke's Law.

Accepted Answer

The rule that a spring's extension grows in direct proportion to the stretching force, so long as the limit of proportionality has not been passed. The graph is a straight line through the origin.

Question 23

Define Spring Constant.

Accepted Answer

The force needed to produce each metre of extension in a spring, quoted in newtons per metre. A stiffer spring carries a larger value and stretches less for the same pull.

Question 24

Define Limit of Proportionality.

Accepted Answer

The point on a force–extension graph past which extension stops keeping step with force, so the plotted line begins to curve away and Hooke's law can no longer be applied.

Question 25

Define Elastic Deformation.

Accepted Answer

A change of shape that reverses completely once the forces are taken away, leaving the object at exactly its original length with nothing permanent about it.

Question 26

Define Inelastic Deformation.

Accepted Answer

A change of shape that fails to reverse fully, leaving the object permanently longer, shorter or bent once the stretching or squashing forces have been removed.

Question 27

Define Elastic Potential Energy.

Accepted Answer

The energy held in a stretched or squashed elastic object, equal to the work done deforming it while Hooke's law still applies, and given back when it springs to shape.

Question 28

Define Moment of a Force.

Accepted Answer

The turning effect produced about a pivot, worked out as the force multiplied by the perpendicular distance from the pivot to the line along which the force acts, in newton metres.

Question 29

Define Principle of Moments.

Accepted Answer

The rule that an object which is balanced has its total clockwise moment about a pivot exactly equal to its total anticlockwise moment about that same pivot.

Question 30

What is Lever?

Accepted Answer

A rigid bar turning about a pivot, arranged so that a modest effort applied far from the pivot delivers a much larger force close to it. It multiplies force, not energy.

Question 31

What is Gear?

Accepted Answer

A toothed wheel meshed with another so that turning one turns the other. A small gear driving a larger one turns it more slowly but with a greater turning effect.

Question 32

Define Centre of Mass.

Accepted Answer

The single point at which an object's entire weight may be treated as acting, which is why a free-body diagram needs only one weight arrow drawn from there.

Question 33

Define Reaction Time.

Accepted Answer

The interval between a driver noticing a hazard and starting to press the brake pedal, usually between 0.2 and 0.9 seconds, and lengthened by tiredness, alcohol, drugs or distraction.

Question 34

Define Thinking Distance.

Accepted Answer

How far a vehicle travels while its driver is still reacting, before the brakes have been touched at all. It scales with speed, so travelling twice as fast doubles it.

Question 35

Define Braking Distance.

Accepted Answer

How far a vehicle carries on from the moment the brakes bite until it halts. Wet or icy roads, worn tyres, tired brakes and a heavier load all lengthen it.

Question 36

What is Momentum?

Accepted Answer

A vector describing the quantity of motion an object carries, obtained by multiplying its mass in kilograms by its velocity in metres per second, in kilogram metres per second.

Question 37

Define Conservation of Momentum.

Accepted Answer

The rule that in a closed system the total momentum before an interaction equals the total afterwards, provided no external resultant force acts. Directions must be included when totalling.

Question 38

Define Pressure in a Fluid.

Accepted Answer

The force a fluid exerts at right angles on each square metre of a surface, quoted in pascals. Within a liquid it climbs with depth and with the density of that liquid.

Question 39

What is Upthrust?

Accepted Answer

The upward force a fluid gives an object placed in it, arising because pressure on the lower surface exceeds pressure on the upper. It matches the weight of fluid displaced.