Mechanics Flashcards
Scalar Quantity
Quantity which has magnitude - distance, time, speed and energy
Vector Quantity
Quantity which has magnitude and direction - displacement, velocity, force and momentum
Displacement
The distance is a given direction
Velocity
The rate of change of displacement
Acceleration
The rate of change of velocity
Force
The rate of change of momentum
Impulse
Change in momentum
Resultant Force
Single force which has the combined effect of two or more forces
Equilibrium
Resultant force acting on an object is equal to zero
- Forces form a closed triangle
- Object is either stationary or moves at constant velocity
Moment
Turning effect of a force
- Moment = Force x perpendicular distance from the line of action of the force to the pivot
Principle of Moments
For an object in equilibrium - sum of all anticlockwise moments about any point must equal the sum of all the clockwise moments about that point
Couple
Pair of equal but opposite coplanar forces
Torque
Turning effect of a couple
Centre of mass
Point where all the mass of an object can be thought to be concentrated
- Use of lines of symmetry to find centre of mass of an object
Displacement time-graph
Displacement (y-axis) against time (x-axis)
Gradient = equal instantaneous velocity
Velocity-time graph
Velocity (y-axis) against time (x-axis)
- Area underneath = displacement
- Gradient = acceleration
Acceleration-time graph
Acceleration (y-axis) against time (x-axis)
- Area = change in velocity
Average velocity
Velocity of an object over a given time period
- Average velocity = total displacement/ total time
Newton’s First Law
Object remains at rest or remains in uniform motion unless acted upon by a force
Newton’s Second Law
Acceleration of an object is directly proportional to the resultant force
Newton’s Third Law
For every action, there is an equal but opposite reaction
Conservation of Momentum
Interacting particle ==> Total momentum is constant provided no external force acts upon the system
Inelastic Collision
A collision where kinetic energy is lost
Elastic Collision
A collision where there is no loss of kinetic energy
Air Resistance
Frictional force acting on an object moving through air, in the opposite direction to the motion of the object
- Air resistance increases with speed
Terminal Speed
Maximum Velocity of a falling object
- No resultant force as the force of air resistance is equal to the weight of the object
Acceleration due to gravity (g)
9.81m/s
Impact Time
The duration for which the impact force acts
Car Safety Features
Crumple zone, airbag and seatbelt
Safety features increase impact time, decreases the deceleration of the vehicle to decrease the impact force experienced by the occupants
Airbag also increases contact area to spread force over a greater area reduces the pressure on the body
Power
Rate of energy transfer
Efficiency
Proportion of total energy input transferred to useful energy output
