7.1 - speed + velocity

what is displacement?

distance in a given direction

what is distance in a given direction?

displacement

what is distance?

how much ground an object has covered during its motion

what is the amount of ground an object has covered during its motion?

distance

what is the unit for distance?

metres (m)

what is the unit for displacement?

metres (m)

what is speed?

change of distance per unit time

what is the change in distance per unit time?

speed

what is velocity?

• change of displacement per unit time

• speed in a given direction

what is the change of displacement per unit time?

velocity

what is the speed in a given direction?

velocity

what is the unit for velocity?

metres per second (m s^-1)

what is the unit for speed?

metres per second (m s^-1)

is distance a vector or scalar quantity?

scalar

why is distance a scalar quantity?

it only has a magnitude

is displacement a vector or scalar quantity?

vector

why is displacement a vector quantity?

it has magnitude and direction

is speed a vector or scalar quantity?

scalar

why is speed a scalar quantity?

it only has a magnitude

is velocity a vector or scalar quantity?

vector

why is velocity a vector quantity?

it has magnitude and direction

how do you convert km h^-1 to m s^-1 ?

here

how do you convert m s^-1 to km h^-1?

here

what is an object moving at constant speed?

an object that travels equal distances in equal amounts of time - e.g., 30 m s^-1 constantly covers 30m every second

what is the equation linking speed, distance, and time?

v = s / t

• v = speed

• s = displacement (can also be distance)

• t = time

v = s / t

equation linking speed, displacement, and time

what is the unit for distance?

d

what is the unit for displacement?

s

what is the unit for speed?

v

what is the unit for velocity?

v

what is the unit for time?

t

what is the speed of an object moving at constant speed on a circle?

v = (2πr) / T

• v = speed

• r = radius of circle

• T = time to move around the circle once (period)

• 2πr = circumference of circle

v = (2πr) / T

speed of an object moving at constant speed on a circle

derive v = (2πr) / T

• v = d / t

• d = circumference = 2πr

• t = T

• therefore v = (2πr) / T

how do you find the average speed of an object moving at changing speeds?

average speed = s / t

average = s / t

average speed of an object moving at constant speeds

what are the two types of speed cameras?

1. measures the speed of a vehicle as it passes the camera

2. linked to a second speed camera and a computer, which works out the average speed between the two cameras

what is the benefit of a speed camera with two separate cameras linked to a computer?

it works out the average speed of the vehicle between the two cameras, meaning it will catch drivers who slow down for a speed camera and speed up again

how do speed cameras track the speed of a passing vehicle?

average speed = s / t

what are the features of a distance-time graph?

here

• y-axis = distance

• x-axis = time

• gradient = speed

what is the y-axis on a distance-time graph?

distance

what is distance on a distance-time graph?

y-axis

what is the x-axis on a distance-time graph?

time

what is time on a distance-time graph?

x-axis

what is the gradient on a distance-time graph?

speed

what is speed on a distance-time graph?

gradient

why is the gradient speed on a distance-time graph?

• gradient = y / x

• = distance / time

• = speed

what is the distance-time graph of an object at constant speed?

• straight line

• constant gradient

here

distance-time graph of an object moving at constant speed here

distance-time graph of an object at constant speed

what is the gradient of distance-time graph of an object constant speed?

constant

what is the distance-time graph of an object moving at changing speed?

here

curved gradient

what is the gradient of distance-time graph of an object moving at changing speed?

curve

distance-time graph of an object moving at changing speed here

distance-time graph of an object moving at changing speed

how do you find the gradient of a distance-time graph of an object moving at changing speed?

• drawing a tangent at the point

• finding the gradient of the tangent

what is constant velocity?

moving at the same speed without changing its direction of motion

how is an object moving when its moving at the same speed without changing its direction of motion?

moving with constant velocity

what will change an object’s velocity?

• changing its direction of motion

• changing its speed

• changing both

what happens when you change an object’s direction of motion?

the object’s velocity changes

what happens when you change an object’s speed?

the object’s velocity changes

what happens when you change both an object’s direction of motion and its speed?

the object’s velocity changes

is an object moving on a circular path at constant or changing velocity?

changing velocity

why is an object moving on a circular path moving at changing velocity?

because its direction is constantly changing, so its velocity is constantly changing

why can displacement be positive or negative?

to signify the direction the object is moving

what is a displacement-time graph?

here

• y-axis = displacement

• x-axis = time

• gradient = velocity

what is the y-axis of a displacement-time graph?

displacement

what is the displacement on a displacement-time graph?

y-axis

what is the x-axis of a displacement-time graph?

time

what is the time on a displacement-time graph?

x-axis

what is the gradient of a displacement-time graph?

velocity

what is velocity on a displacement-time graph?

gradient

what is the displacement-time graph of an object thrown in the air?

here

displacement-time graph of an object thrown in the air here

displacement-time graph of an object thrown in the air

why is the displacement-time graph of an object thrown in the air curved?

• velocity isn’t constant

• velocity is positive when thrown upwards and negative when falling back down

when does a displacement-time graph have a positive gradient?

when the object is moving in a positive displacement so the velocity is positive

what is a displacement-time graph when displacement is positive?

here

gradient is positive

when does a displacement-time graph have a negative gradient?

when the object is moving in a negative displacement so the velocity is negative

what is a displacement-time graph when displacement is negative?

negative gradient

here

when does a displacement-time graph have a straight gradient?

when velocity is constant

what is a displacement-time graph when velocity is constant?

here

gradient is a straight line

what is a displacement-time graph when velocity is changing?

here

gradient is curved

when does a displacement-time graph have a curved gradient?

when velocity is changing

what is the difference between a distance-time graph and a displacement-time graph?

here

displacement-time graphs consider the positive and negative directions of displacement