Kinematics

position

position

an object's distance and direction from a reference point, the coordinate on a number line

Displacement

the change in position of an object, a vector quantity

distance

The length of a path between two points, a scalar quantity

uniform motion

motion with constant velocity

Velocity

Speed in a given direction, a vector quantity (displacement/time)

average speed

total distance divided by total time, a scalar quantity

the graph of constant velocity in a position versus time graph

a straigh line with a slope (non-zero gradient)

the graph of constant velocity in a velocity against time graph

a straight horizontal line

positive velocity

moving forward, position increases

negative velocity

moving backwards, position decreases

instantaneous velocity

the rate of change of position, the gradient in position-time graph, vector quantity

instantaneous speed

the magnitude of instantaneous velocity

Acceleration

the rate of change of velocity, gradient in velocity-time graph, a vector quantity

uniform acceleration

constant acceleration

the graph of unifrom acceleration

a straight line in velocity-time graph

positive acceleration

increase in velocity, the graph is concave up

negative acceleration (deceleration)

decrease in velocity, the graph is concave down

When are average and instantaneous acceleration the same?

constant acceleration

what is the area under the curve in velocity-time graph?

the displacement

graphs of acceleration in position-time graphs

parabolas

what is the area in acceleration-time graph?

change in velocity

when can the equations of kinematics be used?

when the motion is on a straight line with constant acceleration

acceleration of free fall (without air resistance, near the surface)

g = 9,8 m/s^2

what causes the acceleration of free fell?

gravity, the attraction between the earth and the body

the direction of the acceleration of free fall

downwards

projectile motion

the curved path that an object follows when thrown, launched, or otherwise projected near the surface of Earth, throwing a ball upwards and sideways at the same time

how can projectile motions be analyses?

horizontal and vertical vectors

when and why does the horizontal component remain the same in projectile motion?

no force in the horizontal direction >> no acceleration and hence no change in the velocity

when and why is the vertical component changing at all times in projectile motion?

gravitational force causes acceleration downwards at all times >> velocity is changing at all times

projectile

an object that is thrown

position vector

the vector from the origin of a coordinate system to the position of a particle (or an object)

how to see the velocity vectors from the parabola in projectile motion graphs?

they are tangent to the parabola

Range of a projectile

horizontal distance a projectile travels (displacement)

fluid resistance force

a speed dependent force opposing the motion of a body through a fluid

how is the fluid resistance force proportional to speed

magnitude of the force increases with the speed, direclty proportional

terminal speed

the constant speed attained when the resistance force (e.g. air resistance or fluid resistance) becomes equal to the force pushing the body

is projectile motion symmetrical?

yes, if air resistance is not taking into account

How does air resistance affect projectiles?

it will slow the projectile, the maximum height will be smaller, the shape of the motion/the path won't be symmetrical anymore