GCSE Physics
Forces and Newton's Laws Flashcards
39 forces terms GCSE Physics examiners expect you to define precisely
39 cards~10 min
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All 39 GCSE Physics Forces and Newton's Laws flashcards
The full deck in writing, listed A to Z. Read it through if the topic is new, then use the cards above to test yourself without looking.
- Braking Distance
- 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.For example: Ice can stretch it to roughly ten times its value on a dry road.
- Centre of Mass
- 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.For example: For a uniform metre rule this point sits at the 50 cm mark.
- Conservation of Momentum
- 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.For example: Two skaters pushing apart glide off with equal and opposite momenta.
- Contact Force
- A force that can only act while two objects are physically touching each other, disappearing the instant they separate.For example: Friction, air resistance, tension in a rope and the normal contact force from a surface.
- Drag
- 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.For example: A cyclist crouches low over the handlebars to cut the drag from the air.
- Elastic Deformation
- 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.For example: A stretched rubber band that snaps back to the size it started at.
- Elastic Potential Energy
- 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.For example: A drawn catapult stores it, then transfers it to the stone's kinetic store.
- Equilibrium
- 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.For example: A parked car: weight downwards, normal contact force upwards, nothing changing.
- Free-Body Diagram
- 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.For example: A skydiver drawn with one long arrow down for weight and one arrow up for drag.
- Friction
- 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.For example: Brake pads and the wheel disc grow hot on a long descent.
- Gear
- 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.For example: A low gear on a bicycle trades speed for the extra turning effect needed on a hill.
- Gravitational Field Strength
- 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.For example: The lunar value is close to 1.6 N/kg, about a sixth of the value at the Earth's surface.
- Hooke's Law
- 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.For example: Doubling the load on such a spring doubles how far it stretches.
- Inelastic Deformation
- 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.For example: A spring pulled far past its limit that stays stretched afterwards.
- Inertia
- 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.For example: Books slide off a car seat when the driver brakes sharply.
- Inertial Mass
- 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.For example: Given equal pushes, the trolley that speeds up least has the larger inertial mass.
- Lever
- 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.For example: A crowbar, a spanner and a wheelbarrow all work in this way.
- Limit of Proportionality
- 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.For example: Loading a spring beyond this point bends the graph away from the straight line.
- Mass
- 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.For example: A 2 kg bag of sugar stays 2 kg on Earth, on the Moon and in deep space.
- Moment of a Force
- 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.For example: A 20 N push applied 0.5 m from a door's hinge gives a moment of 10 N m.
- Momentum
- 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.For example: A 1200 kg car travelling at 15 m/s carries 18 000 kg m/s of momentum.
- Newton
- 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.For example: A typical adult on Earth has a weight of about 600 N.
- Newton's First Law
- 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.For example: A puck on frictionless ice would keep sliding at the same speed indefinitely.
- Newton's Second Law
- 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.For example: The same engine force accelerates an empty van more than a fully loaded one.
- Newton's Third Law
- 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.For example: A swimmer pushes water backwards and the water pushes the swimmer forwards.
- Non-Contact Force
- A force acting between two objects that are separated, carried across the gap by a field rather than by anything touching.For example: Gravitational attraction, magnetic attraction and electrostatic repulsion all act at a distance.
- Normal Contact Force
- 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.For example: The upward push of the floor on your feet while you stand still.
- Pressure in a Fluid
- 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.For example: A dam is built thicker at its base, where the water presses hardest.
- Principle of Moments
- 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.For example: A lighter child sits further out on a see-saw to balance a heavier one.
- Reaction Time
- 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.For example: Using a phone at the wheel can more than double this interval.
- Resultant Force
- 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.For example: A 30 N drive with 12 N of drag against it leaves 18 N forwards.
- Scalar Quantity
- 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.For example: Mass, temperature, distance, speed and energy are all scalars.
- Spring Constant
- 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.For example: A spring needing 12 N to stretch 0.04 m has a spring constant of 300 N/m.
- Terminal Velocity
- 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.For example: A parachutist falls near 55 m/s, then settles at a far slower value once the canopy opens.
- Thinking Distance
- 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.For example: At 30 mph a driver covers roughly 9 m before the brakes go on.
- Upthrust
- 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.For example: A ship floats once upthrust has grown equal to its weight.
- Vector Quantity
- 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.For example: Displacement, velocity, acceleration, force and momentum are all vectors.
- Weight
- 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.For example: A 5 kg school bag has a weight of roughly 49 N at the Earth's surface.
- Work Done
- 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.For example: Dragging a crate 3 m with a steady 20 N force does 60 J of work.