Speed, velocity and acceleration

Core Define speed and calculate speed from Total distance/total time Plot and interpret a speed/time graph or a distance/ time graph Recognise from the shape of a speed/time graph when a body is – at rest – moving with constant speed – moving with changing speed Calculate the area under a speed/time graph to work out the distance travelled for motion with constant acceleration Demonstrate some understanding that acceleration is related to changing speed

Supplement Distinguish between speed and velocity

You will learn How to calculate average speed The difference between speed and velocity How to calculate acceleration How to interpret velocity-time graphs.

Speed and velocity Speed is a _______________ quantity. Speed is measured in __________ (units). The average speed of an object can be calculated using the equation: Instantaneous speed is more difficult to measure but can be found by looking at the _________________ of a _____________ vs . time graph.

Velocity Velocity is a _______________ quantity it has both magnitude and _________________. Velocity is measured in __________ (units). Hence a change in _____________ causes a change in velocity. E.g. 1 A car going at a constant ___________ in a circle has a changing velocity. E.g. 2 An object travelling at 10m/s that returns to its original position has an average velocity of ___ m/s.

Acceleration Acceleration is a _______________ quantity. Acceleration is measured in __________ (units). The Acceleration of an object can be calculated using the equation: Acceleration = __________ Acceleration can be found by looking at the _________________ of a _____________ vs . time graph. A negative Acceleration is called ___________

Activities Read p 26+27 Answer questions on page 27

Velocity time graphs

Velocity time graphs. Velocity – time graphs can show information about the motion of an object in more ________ The _____________ of the line on a v-t graph tells us about the acceleration. A greater acceleration is shown by a _________ line. If acceleration is constant the line is _________ An increasing acceleration is shown by a line that _____________ _____ A decreasing acceleration is shown by a line that _____________ _____ The distance travelled by an object can be determined by the __________ ________ _______ ________

To do P29 q 2

Experiment

Supplement Recognise linear motion for which the acceleration is constant and calculate the acceleration Recognise motion for which the acceleration is not constant

You will learn How to recognise constant acceleration on a speed-time graph How to calculate acceleration from a speed – time graph How to recognise non constant acceleration from a speed time graph

Practice P35 q 1&2

v = at when applied to an object accelerating uniformly from rest What is the equation for acceleration? acceleration = Change in velocity / time So Change in velocity = ? acceleration x time Change in velocity = ? Final velocity – initial velocity (v-u) What if initial velocity is zero? v = at

Summary questions A car accelerates from 10 m/s to 25 m/s over a period of 5 seconds. What is the acceleration? 2. A wombat falls out of a tree into a vat of custard. It starts from rest, and accelerates at 10 m/s2 until it lands in the custard 5 seconds later. How fast is it going when it hits the custard?

Chapter 18 : Velocity and Acceleration 1 Answers Chapter 18 : Velocity and Acceleration 1 A car accelerates from 10 m/s to 25 m/s over a period of 5 seconds. What is the acceleration? 2. A wombat falls out of a tree into a vat of custard. It starts from rest, and accelerates at 10 m/s2 until it lands in the custard 3 seconds later. How fast is it going when it hits the custard? Acceleration = (change in velocity) ÷ time = (25 – 10) ÷ 5 = (15) ÷ 5 = 3 m/s2 Acceleration = (change in velocity) ÷ time 10 = (v – 0) ÷ 3 So v = 3 × 10 = 30 m/s That’s over 60 mph – ouch!

Velocity and Acceleration Use these words to label the graphs correctly. stopped slow fast fast stopped accelerating decelerating

Velocity and Acceleration Answers Velocity and Acceleration Use these words to label the graphs correctly. stopped slow fast fast stopped accelerating decelerating accelerating decelerating fast stopped fast stopped slow