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neurologyYou need to know

• A scalar quantity has magnitude only, whereas a vector quantity has both magnitude and direction.
• Distance, speed, mass, time, energy and temperature are scalar quantities; displacement, velocity, acceleration, force, weight and momentum are vector quantities.
• A force is a push or pull on an object caused by an interaction, and it can change an object’s speed, direction of motion, or shape.
• Contact forces require objects to touch, such as friction, air resistance, tension and normal contact force; non-contact forces act at a distance, such as gravitational, electrostatic and magnetic forces.
• The resultant force is the single force that has the same effect as all the forces acting on an object combined.
• An object is in equilibrium when the resultant force on it is zero, so its velocity does not change.
• Weight is the gravitational force on an object, acts vertically downwards, and is calculated using `W = mg`, where gravitational field strength on Earth is about `9.8 N/kg`.
• Work is done when a force moves an object through a distance, and the energy transferred is calculated using `W = Fs` when the force acts in the direction of motion.
• One joule is the work done when a force of `1 N` moves an object through a distance of `1 m` in the direction of the force.
• When work is done against friction, energy is transferred to the thermal store of the objects and their temperature increases.
• An object can be stretched, compressed or bent only when more than one force acts on it, because a single unbalanced force would accelerate the object rather than deform it alone.
• Elastic deformation is deformation that is reversed when the forces are removed, whereas inelastic deformation is permanent deformation.
• For a spring within its limit of proportionality, force is directly proportional to extension and is described by Hooke’s law, `F = ke`.
• The work done in stretching or compressing a spring is the elastic potential energy stored and is calculated using `E = \frac{1}{2}Fe` or `E = \frac{1}{2}ke^2`.
• Distance is the total length travelled, while displacement is the straight-line distance from start to finish in a specified direction.
• Speed is the rate of change of distance, while velocity is the rate of change of displacement in a specified direction.
• Typical speeds are about `1.5 m/s` for walking, `3 m/s` for running, `6 m/s` for cycling, `25 m/s` for a car, and `330 m/s` for sound in air.
• In circular motion at constant speed, the velocity changes because the direction of motion changes continuously.
• On a distance-time graph, the gradient represents speed; on a velocity-time graph, the gradient represents acceleration and the area under the graph represents displacement.
• Momentum is calculated using `p = mv`, and the total momentum of objects in a closed system is conserved before and after a collision or explosion.

• Classify physical quantities as scalars or vectors by checking whether direction is needed as well as magnitude.
• Represent vector quantities using scale diagrams with arrows whose lengths show magnitude and whose arrowheads show direction.
• Calculate a resultant vector by adding vectors head-to-tail or by subtracting opposing vectors, including stating the size and direction of the final vector.
• Resolve a force into horizontal and vertical components using right-angled trigonometry, selecting sine or cosine from the angle given.
• Calculate weight, work done, elastic potential energy, speed, acceleration, resultant force and momentum by substituting values into the correct equations with standard units.
• Interpret motion graphs by using gradients to find speed or acceleration and areas under velocity-time graphs to find displacement.
• Apply the suvat equations for uniformly accelerated motion by selecting the correct equation from the known and unknown quantities.
• Apply Newton’s laws to explain motion, including equilibrium, acceleration from a resultant force, and action-reaction force pairs.
• Explain terminal velocity using a force diagram, describing how weight and drag change until the resultant force becomes zero.
• Solve conservation of momentum problems by equating total momentum before and after an interaction in a closed system.