Scalar quantity: A quantity that has only magnitude
Vector quantity: A quantity that has magnitude as well as direction
Acceleration is a vector quantity
Mass is a scalar quantity
Difference between mass and weight:
Mass is scalar and not dependent on gravity
Weight is a vector and depends on gravitational field strength (W = mg)
If an object is in equilibrium:
Sum of anti-clockwise moments = sum of clockwise moments (principle of moments)
Object is not accelerating, so is either stationary or moving at a constant velocity
How forces acting on an object can be shown to be in equilibrium:
Adding horizontal and vertical components of forces, showing they equal zero
For 3 forces, draw a scale diagram forming a closed triangle if the object is in equilibrium
Moment: A turning force, force multiplied by perpendicular distance from point to line of action of the force
Couple: A pair of equal and opposite coplanar forces
Centre of mass: Point through which all mass of an object acts, for a uniform object, the centre of mass is at the centre of the object
Velocity: Change in displacement per unit of time, instantaneous velocity found by measuring gradient of tangent to a displacement-time graph
Area under a velocity-time and acceleration-time graph:
Displacement travelled and velocity respectively
As speed increases, air resistance increases (proportional to the square of the speed)
Horizontal velocity of a ball projected off a castle at 6m/s remains the same until it hits the ground
SUVAT equations reflect that all objects fall at the same rate because mass is not included in the equations
In projectile motion, vertical acceleration is equal to gravitational field strength (g)
Terminal velocity: When forces acting on a falling object become balanced, acceleration becomes zero and object moves at maximum velocity
Friction: Resistance to motion between an object and a surface or fluid, force that acts opposite to movement
Newton's third law states 'every action force has an equal and opposite reaction force'
Newton's second law: F = ma, where F is force applied and a is acceleration
Newton's first law: An object stays moving at a constant velocity until a force acts upon it
Difference between elastic and inelastic collisions:
Elastic: Kinetic energy before = kinetic energy afterwards
Inelastic: Kinetic energy at the end is not equal to the kinetic energy at the start
Equation to calculate momentum: Momentum = mass × velocity
Linear momentum is always conserved, not only in elastic collisions
Rate of change of momentum is described as force
Impulse: Change in momentum, F∆t = ∆mv
Area under a force-time graph represents impulse, the change in momentum
Fs cos( 𝜽 ) = The work done / the energy transferred
Rate of work done is equal to power
Efficiency = Useful output power / input power
Principle of conservation of energy: Energy cannot be created or destroyed, only transferred into other forms, total energy in a closed system remains constant
Lift: Upward force acting on objects in a fluid, caused by object changing direction of fluid flow, acts perpendicular to fluid flow
Hooke’s law:
Extension (∆L) is directly proportional to force applied (F), given that the environmental conditions are kept constant
F= k∆L
k is the stiffness constant in Nm^-1
Equation to calculate density:
Density = Mass / Volume
Density units: kgm^-3
Mass: kg
Volume: m^3
Tensile stress:
The force applied per unit cross-sectional area
Stress = force / CSA
Stress units: Nm^-2
Force units: N
Cross-sectional area units: m^2
Tensile strain:
A measure of how the material stretches: the extension (ΔL) divided by the original length (L), strain has no units
Strain = ΔL / L
Difference between elastic and plastic deformation:
Elastic deformation: when the force is removed the object will return to its original shape
Plastic deformation: after the load is removed the object will not return to its original shape
Breaking stress:
The minimum stress needed to break a material
Brittle material:
Doesn’t deform plastically but breaks when the stress reaches a certain value
Elastic limit:
The force above which the material will be plastically deformed (permanently stretched)