Physics Definitions and Terms
1
,1. Kinematics
Vector – a physical quantity that has both magnitude and direction.
(position, displacement, velocity, acceleration, momentum, impulse…)
Scalar – a physical quantity that has magnitude only. (distance, speed,
mass, time…)
Resultant vector – the single vector which has the same effect as the
original vectors acting together.
Position – a vector quantity that points from the reference point as the
origin. ALWAYS RELATIVE TO A REFERENCE POINT!!! (0m)
Distance – the length of path travelled.
Direction / bearing is measured in (°) in a clockwise direction from
reference point. (x)km on a bearing of (y)°.
Displacement – the change in position of a body.
Speed – the rate of change of distance.
Velocity – the rate of change of displacement.
Instantaneous velocity – velocity at a particular instant in time.
Average velocity – velocity of an object over its entire distance / over a
longer time interval.
Acceleration – the rate of change of velocity.
WHEN USING EQUATIONS OF MOTION, ALWAYS CHOOSE A
DIRECTION AS POSITIVE!!
Equations of motion in a horizontal plain – have to work out acceleration.
Equations of motion in a vertical plain – a = +/- 9,8m.s-2 near the surface.
Rule 1 – the gradient of a position(x) vs time(t) graph is equal to
velocity(v).
Rule 2 – the gradient of a v vs t graph is equal to acceleration(a).
Rule 3 – the area under a v vs t graph is equal to displacement(∆x).
Also, the area under an a vs t graph is equal to ∆x.
x vs t → a vs t – only look at slant of curves.
v vs t → a vs t – just see if it’s going down, up or stationery (gradient).
2
, Gravitational force (Fg) = weight of the object.
ACCELERATION DUE TO GRAVITY IS ALWAYS DOWN.
Free falling object:
Accelerates downwards at 9.8m.s-2 near the surface of the Earth.
The acceleration does not depend on mass.
Only force acting on it is Fg.
Will NEVER reach terminal velocity.
Objects with different masses fall with the same acceleration. Surface
area only affects the rate of fall of the object.
Terminal velocity – when an object no longer accelerates and it reaches
constant velocity.
Projectiles take the same time to reach highest point as the time to come
back down to point of launch.
Balloon is stationery and something drops – vi = 0m.s-1.
Balloon at constant velocity up and obj dropped – vi = speed of balloon.
Balloon at constant velocity but obj is thrown down – vi = difference
between the speed of the balloon and the speed the obj was thrown.
Bearing is ALWAYS measured up until the resultant force line (90° +/-
angle) when using a diagram.
When resolving the vector into its parallel and perpendicular
components, draw the tail-to-tail diagram.
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1
,1. Kinematics
Vector – a physical quantity that has both magnitude and direction.
(position, displacement, velocity, acceleration, momentum, impulse…)
Scalar – a physical quantity that has magnitude only. (distance, speed,
mass, time…)
Resultant vector – the single vector which has the same effect as the
original vectors acting together.
Position – a vector quantity that points from the reference point as the
origin. ALWAYS RELATIVE TO A REFERENCE POINT!!! (0m)
Distance – the length of path travelled.
Direction / bearing is measured in (°) in a clockwise direction from
reference point. (x)km on a bearing of (y)°.
Displacement – the change in position of a body.
Speed – the rate of change of distance.
Velocity – the rate of change of displacement.
Instantaneous velocity – velocity at a particular instant in time.
Average velocity – velocity of an object over its entire distance / over a
longer time interval.
Acceleration – the rate of change of velocity.
WHEN USING EQUATIONS OF MOTION, ALWAYS CHOOSE A
DIRECTION AS POSITIVE!!
Equations of motion in a horizontal plain – have to work out acceleration.
Equations of motion in a vertical plain – a = +/- 9,8m.s-2 near the surface.
Rule 1 – the gradient of a position(x) vs time(t) graph is equal to
velocity(v).
Rule 2 – the gradient of a v vs t graph is equal to acceleration(a).
Rule 3 – the area under a v vs t graph is equal to displacement(∆x).
Also, the area under an a vs t graph is equal to ∆x.
x vs t → a vs t – only look at slant of curves.
v vs t → a vs t – just see if it’s going down, up or stationery (gradient).
2
, Gravitational force (Fg) = weight of the object.
ACCELERATION DUE TO GRAVITY IS ALWAYS DOWN.
Free falling object:
Accelerates downwards at 9.8m.s-2 near the surface of the Earth.
The acceleration does not depend on mass.
Only force acting on it is Fg.
Will NEVER reach terminal velocity.
Objects with different masses fall with the same acceleration. Surface
area only affects the rate of fall of the object.
Terminal velocity – when an object no longer accelerates and it reaches
constant velocity.
Projectiles take the same time to reach highest point as the time to come
back down to point of launch.
Balloon is stationery and something drops – vi = 0m.s-1.
Balloon at constant velocity up and obj dropped – vi = speed of balloon.
Balloon at constant velocity but obj is thrown down – vi = difference
between the speed of the balloon and the speed the obj was thrown.
Bearing is ALWAYS measured up until the resultant force line (90° +/-
angle) when using a diagram.
When resolving the vector into its parallel and perpendicular
components, draw the tail-to-tail diagram.
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