Chapter 1 Flashcards
Motion Forces and Energy
Acceleration of free fall, g
For an object near to the surface of the Earth this is approximately constant and is approximately 9.8 m/s²
Accuracy
An accurate measurement is one that is close to its true value
Air resistance
Frictional force opposing the motion of a body moving in air
Centre of gravity
The point at which all the mass of an object’s weight can be considered to be concentrated
Density
The mass per unit volume
Energy
Energy may be stored as kinetic, gravitational potential, chemical, elastic (strain), nuclear, electrostatic or internal (thermal)
Equilibrium
When there is no resultant force and no resultant moment on an object
Extension
Change in length of a body being stretched
Friction
Force which opposes one surface moving, or trying to move, over another surface
Gravitational field strength
The force per unit mass
Mass
A measure of the quantity of matter in an object at rest relative to an observer
Moment of a force
Moment = force × perpendicular distance from the pivot
Pressure
The force per unit area
Power
The work done per unit time and the energy transferred per unit time
Non-renewable
Cannot be replaced when used up
Principle of conservation of energy
Energy cannot be created or destroyed; it is always conserved
Principle of moments
States when a body is in equilibrium; the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about the same point
Random error
Error introduced by the person taking the measurement
Speed
The distance travelled per unit time
Renewable
Can be replaced; cannot be used up
Systematic error
Error introduced by the measuring device
Weight
A gravitational force on an object that has mass
Velocity
Speed in a given direction
Work
A measure of the amount of energy transferred. Work done = force × distance moved in the direction of the force. SI unit is the joule (J
Acceleration
Change of velocity per unit time
Deceleration
A negative acceleration; velocity decreases as time increases
Efficiency
(useful energy output / total energy input) × 100%
(useful power output / total power input) × 100%
Impulse
Force × time for which force acts
Momentum
Mass × velocity
Limit of proportionality
The point at which the load-extension graph becomes non-linear
Principle of conservation of momentum
When two or more bodies interact, the total momentum of the bodies remains constant provided no external forces act
Resultant vector
A single vector that has the same effect as the two vectors combined
Resultant force
The rate of change in momentum per unit time
Scalar
A quantity with magnitude only
Spring constant
Force per unit extension
Terminal velocity
Constant velocity reached when the air resistance upwards equals the downward weight of the falling body
Vector
A quantity which has both magnitude and direction
