BRAINCAKEForces
Revision notes for Forces in OCR Combined Science A (J250). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.
- Measuring distance and timeTo find how fast something moves you need two measurements: how far it goes and how long it takes.
- Calculating speed from distance-time graphsSpeed tells you how far an object travels each second.
- Converting units and calculating ratesCalculations in physics work best in SI units: metres for distance, seconds for time and metres per second for speed.
- Vectors and scalars: displacement and velocityA scalar quantity has size (magnitude) only.
- Interpreting motion graphsOn a distance-time graph the gradient is the speed.
- Area under a velocity-time graphThe area between a velocity-time line and the time axis equals the distance travelled.
- Average speed for non-uniform motionIn most real journeys the speed does not stay the same.
- Distance, time and speed: uniform motion and uniform accelerationIn uniform motion an object travels at a constant speed in a straight line.
- Ways objects interactObjects interact when they push or pull on each other.
- Interaction pairs of forcesA force never acts alone.
- Forces as vectors and free body diagramsA vector is a quantity that has both size and direction.
- Newton's first lawNewton's first law says that an object stays at rest, or keeps moving at a constant velocity, unless a resultant force acts on it.
- Vector diagrams, resultants and equilibriumForces can be added using arrows drawn to scale.
- Forces on a falling object and terminal velocityTo describe the forces on an isolated object, consider only the forces acting on that object.
- Resultant forces and free body diagramsA free body diagram shows a single object on its own, with an arrow for every force acting on it.
- Balanced forces and a zero resultantSometimes the forces on an object are balanced.
- Newton's Second Law: F = maNewton's Second Law links force, mass and acceleration.
- Inertia and inertial massObjects resist changes to their motion.
- Momentum and conservation of momentumMomentum is a property of a moving object.
- Work done, force and distanceWhen a force moves an object, energy is transferred.
- Stored energy and energy transfersEnergy can be stored in a stretched spring or in an object lifted above the ground.
- Power as the rate of energy transferSome devices transfer energy faster than others.
- Newton's Third Law: equilibrium and non-equilibriumNewton's Third Law says that when object A exerts a force on object B, object B exerts a force on object A that is equal in size and opposite in…
- Circular motion and changing velocitySpeed tells us only how fast an object moves.
- Forces needed to stretch, bend or compressA single force on a free object usually just makes it move.
- Elastic and plastic deformationWhen stretching forces act on an object, its shape changes.
- Force and extension for a springThe extension of a spring is how much longer it gets.
- Linear and non-linear force-extensionOn a force-extension graph, a linear relationship is a straight line through the origin.
- Calculating the spring constantFor a spring that obeys Hooke's law, the force exerted is found with the equation force = spring constant × extension, or F = k × e.
- Work done in stretching a springStretching a spring needs a force to act over a distance, so work is done on the spring.
- Gravitational fields and attractionEvery object that has mass is surrounded by a gravitational field.
- Weight and gravitational field strengthWeight is the force acting on an object because of the gravitational field it is in.
- Acceleration in free fallAn object is in free fall when the only force acting on it is its weight.