physics - kinematics

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JemmyG7

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Kinematics refers to the bunch of mechanics in physics that is concerned with the motion of a body, or a system of bodies, without consideration of its mass or the forces which cause the motion
Distance is the total length travelled by the body regardless of the direction of motion.
Distance is a scaler quantity; the direction of travel does not matter, only the magnitude does.
The S.I. unit of distance is metre (m).
Displacement is the distance measured in a straight line in a specified direction.
Displacement is a vector quantity; meaning that both magnitude and direction needs to be stated.
The S.I. unit of displacement is metre (m).
Speed of a body is defined as the distance traveled per unit time.
Speed = distance traveled / time taken
Speed is a scaler quantity.
The S.I. unit of speed is metre per second ( $ms^-1$ )
Average speed = total distance traveled / total time taken
Instantaneous speed is defined as the speed of the body at any given point in time.
In order to fully describe the motion of a body, we need to describe both the speed and direction of the body, using velocity.
Velocity = change in displacement / time taken
(change can be represented with a triangle, a delta sign)
The symbol for displacement (in equations) is s
Average velocity = total displacement / total time taken
Acceleration is defined as the rate of change of velocity or the change in velocity per unit time.
Acceleration = change in velocity / time taken
Acceleration is a vector quantity.
S. I. unit for acceleration is metre per second square (m s-2)
Rectilinear motion is when a body moves in a straight line or parallel to one. The body moves in one-dimension and can only move in two possible directions, with one direction being the opposite of the other.
When vector quantities are involved in a question, we have to assign one direction as positive and the other as negative.
Graphs are used in Physics to give a visual representation of relationships between different physical quantities.
In kinematics, graphs can be used to show how displacement, velocity and acceleration of a body change with time
The gradient of a displacement-time graph gives the velocity of the body
If the gradient of the displacement-time graph is a constant value (a straight line), the velocity of the body is constant (no acceleration). It moves with uniform velocity or is at rest.
If the gradient of the displacement-time graph is not a constant value (eg, a curved line), the velocity of the body is not constant (non-uniform)
On a displacement-time graph, a gentle to steep slope reflects increasing velocity while a steep to gentle slope indicates a decreasing velocity.
Increasing gradient = increasing magnitude of velocity
Decreasing gradient = decreasing magnitude of velocity
When a displacement-time graph has a positive gradient, the body is moving in a positive direction and has positive velocity.
When a displacement-time graph has a negative gradient, the body is moving in the negative direction and has a negative velocity.
For all graphs, the gradient of a curve can be described in two parts:
Sign of the gradient of the curve (positive, negative or zero)
Changes to the magnitude of the gradient (increasing, decreasing or constant)
The gradient of the velocity - time graph is the change in velocity over the change in time, the same as acceleration
The gradient of the velocity - time graph is the acceleration
The area under velocity - time graphs is the change in displacement
A body moving with constant acceleration will be reflected with a straight line (constant gradient) on a velocity - time graph as the body moves proportionally with time.
Non-uniform acceleration, also known as terminal velocity is reflected with a curve on the velocity - time graph.
If the change in velocity occurs at an increasing rate, the object is said to be experiencing increasing acceleration.
On a velocity - time graph, it will be reflected as
If the change in velocity occurs at an decreasing rate, the object is said to be experiencing decreasing acceleration.
On a velocity - time graph, it will be reflected as
A velocity - time graph with a 0 gradient indicates that an object is at rest (line is on the x axis, y=0) or moving at a constant velocity (ie, no acceleration or deceleration)