Physics P2 Forces

P1.1: The particle model P2.1 motion

pLAN Progress stickers Expectations Review Recap Questions

P2.1a & b – Speed, distance & time 18/11/2018 P2.1a & b – Speed, distance & time Objective To be able to describe how to measure distance and time in a range of scenarios. To be able to calculate the speed of an object from the measurements of distance and time. Can you give an estimate of these distances & times? Starter - what would you use to measure: The length of a table, the diameter of a CD, the length of a hockey pitch, the distance from Bury to Manchester. The time taken to run 100m, the amount of time in a school day, the time between one full moon and the next.

Speed, Distance & Time What do we measure speed in? What do we measure distance in? What do we measure time in? What does miles per hour mean? If you were to travel 60 miles in an hour, what is your speed? If you were to travel 60 miles in 2 hours, what is your speed? If you were to travel 60 miles in 3 hours, what is your speed?

How did you find the speed? All you did was distance ÷ time. So we now have a formula: Speed = Distance ÷ Time The standard units (what we measure stuff in) are: Speed – metres per second (m/s) Distance – metres (m) Time – seconds (s) What does this line mean? What does per mean? They both just mean divide!

Speed, distance & time - The formula Divide! You need to remember this formula! How? Use what you already know! What is speed measured in? metres per second (m/s) So the formula for speed has to be something in metres divided by something in seconds! What is measured in metres? What is measured in seconds? So, Speed = Distance ÷ Time What does this line mean? Wahooooo!

Activity – How far? How Fast? Lets plan an experiment to calculate how fast we can walk/run. Where should we do the experiment? What do we need? How are we going to record our results? Are we going to do the experiment more than once? How do we calculate the speed? How do we find an average of multiple results?

How far? How fast? The time two students take to run _____ metres. The average speed of Student 1 was ______ metres per second. The average speed of Student 2 was ______ metres per second. Attempt Student 1 Time (s) Student 1 Speed (m/s) Student 2 Time (s) Student 2 Speed (m/s) 1 2 3

Speed, distance time booklet Question 1

P2.1 b – Speed, distance & time 18/11/2018 P2.1 b – Speed, distance & time Objective To investigate how the angle of a ramp affects the speed of a trolley rolling down it. Starter What is the standard unit of speed? Are there other units we can measure speed in? What are they?

Trolley on a ramp What are we going to change? What are we going to keep the same? How are we going to measure the height of the top of the slope? How are we going to record our results?

Trolley on a ramp - results Height (m) Time 1 (s) Time 2 (s) Time 3 (s) Average Time (s) Average Speed (m/s) Extension: Was the trolley always moving at the same speed? The distance the trolley travelled was _______ metres. Average speed = Distance ÷ Time

Height (m) Max Time (s) Min Speed (m/s) Min Time (s) Max Speed (m/s) Average Speed (m/s)

Trolley on a ramp - conclusion The greater the height, the ___________ the time. Therefore the __________ the speed. Was the trolley travelling at the same speed all of the time? Write a method to measure the acceleration of the car down the ramp.

Acceleration Acceleration = Change in Speed (m/s) (m/s2) Time (s)

Questions d = 100m t = 10s speed = d = 1500m t = 300s speed = d = 24m s = 8 m/s time = s = 33 m/s t = 3s distance = Change in speed = 44m/s time = 4s acceleration = Acceleration = 10m/s2 time = 15s change in speed = Change in speed = 15m/s acceleration = 5m/s2 time =

Acceleration on a ramp - results Height (metres) Time (s) Distance Time Final Velocity (m/s) Acceleration

18/11/2018 P2.1 c – SI units Objective To be able to convert non-SI units to SI units. Starter How many centimetres are in a metre? How many metres are in a kilometre? How many kilometres are in a mile?

Converting units There are 1.6km in a mile. How many kilometres in 15 miles? How many kilometres in 25 miles? If a car is travelling at 30 miles per hour (mph), what is it’s speed in kilometres per hour (km/h)?

Will the answer be greater or smaller? Converting units There are 1.6km in a mile. If a car is travelling at 30 miles per hour (mph), what is its speed in metres per second (m/s)? Need to convert miles  km (multiply by 1.6) 30 x 1.6 = 48 km/h = 48000 m/h Need to convert per hour  per second How many seconds in an hour? 60 seconds x 60 minutes = 3600s 48000 ÷ 3600 =13.3 m/s Think! Will the answer be greater or smaller?

examples There are 1.6km in a mile. There are 3600s in an hour. Convert the following, to m/s: 20 km/h 40 miles per hour 60 miles per hour

18/11/2018 P2.1d – vectors & scalars Objective To understand the difference between scalars and vectors. https://www.youtube.com/watch?v=A05n32Bl0aY Starter: What is the difference between a scalar and a vector.

Scalar quantities are measured with numbers and units. What is a scalar? Scalar quantities are measured with numbers and units. Photo credit (all): © 2009 Jupiterimages Corporation length temperature time (e.g. 16 cm) (e.g. 102 °C) (e.g. 7 s) 25

What is a vector? Vector quantities are measured with numbers and units, but also have a specific direction. Photo credit (left and middle): © 2009 Jupiterimages Corporation Photo credit (right): © Shutterstock 2009, Vladimir Daragan acceleration displacement force (e.g. 30 m/s2 upwards) (e.g. 200 miles northwest) (e.g. 2 N downwards) 26

Comparing scalar and vector quantities 27

Speed or velocity? Distance is a scalar and displacement is a vector. Similarly, speed is a scalar and velocity is a vector. Speed is the rate of change of distance in the direction of travel. Speedometers in cars measure speed. Velocity is a rate of change of displacement and has both magnitude and direction. Averages of both can be useful: average speed distance time average velocity displacement time = =

Vector or scalar? 29

Next Steps Car and ramp experiment – write a conclusion 19/6/17 – Dissolving is an example of a ____________ change. 6/6/17 - Write out these numbers in standard form: 2100000 0.0005 45000

P2.1E – distance-time & velocity-time graphs 18/11/2018 P2.1E – distance-time & velocity-time graphs Objective To be able to interpret distance-time and velocity-time graphs. To be able draw to distance-time, velocity-time and displacements-time graphs. Starter: Which of these are scalars and which are vectors? length velocity speed temperature distance displacement force mass energy acceleration

Speed, distance & Time What are the SI units of speed? What is the formula? Did you use the units to help you?

Distance-time graphs DISTANCE – TIME GRAPHS 2) Horizontal line = 4) Diagonal line downwards = 40 30 20 10 Distance (metres) 3) Steeper diagonal line = Diagonal line = 20 40 60 80 100 Time/s

Distance-time graphs Distance (metres) Time/s 40 30 20 10 Distance-time graphs Distance (metres) 20 40 60 80 100 Time/s What is the speed during the first 20 seconds? How far is the object from the start after 60 seconds? What is the speed during the last 40 seconds? When was the object travelling the fastest?

Velocity-time graphs VELOCITY – TIME GRAPHS 1) Upwards line = 80 60 40 20 4) Downward line = Velocity (m/s) 3) Upwards line = 2) Horizontal line = 10 20 30 40 50 Time (s)

How fast was the object going after 10 seconds? 80 60 40 20 Velocity (m/s) 10 20 30 40 50 Time (s) How fast was the object going after 10 seconds? What is the acceleration from 20 to 30 seconds? What was the deceleration from 30 to 50s? How far did the object travel altogether?

Speed vs. Velocity Speed is simply how fast you are travelling… This car is travelling at a speed of 20m/s Speed vs. Velocity Velocity is “speed in a given direction”… This car is travelling at a velocity of 20m/s east

P2.1f – Non-uniform Motion 18/11/2018 P2.1f – Non-uniform Motion Objective To calculate the average speed of an object not travelling uniformly. Starter: Calculate the distance travelled by a car travelling at 7m/s for 1 hour.

Acceleration Acceleration = change in velocity (in m/s) (in m/s2) time taken (in s) A cyclist accelerates at a constant rate from 0 to 10m/s in 5 seconds. What is her acceleration? A ball is dropped and uniformly accelerates downwards at a rate of 10m/s2 for 12 seconds. How much will the ball’s velocity increase by? A car accelerates from 10 to 20m/s with a constant acceleration of 2m/s2. How long did this take? A rocket accelerates uniformly from 1,000m/s to 5,000m/s in 2 seconds. What is its acceleration?

Non-uniform Motion You should be able to use a distance-time graph to describe an object's motion when it's accelerating or decelerating. Remember the steeper the gradient the faster the speed. This graph shows acceleration:

Non-uniform motion This graph shows deceleration:

Non-uniform motion How do we calculate the distance travelled by an object in a set amount of time? Distance = (Average) Speed x Time When an object is travelling at a constant speed it’s average speed is just that value. For example if a car is constantly travelling at 5 m/s then it’s average speed is just 5 m/s. But what happens if the car is changing speed? We need to find it’s average speed.

Non-uniform motion If Bradley Wiggins accelerates at a constant rate from 0 m/s to 10 m/s, what is his average speed? How do we normally calculate an average? Add the numbers and divide by how many there are. 0 + 10 = 10 10/2= 5 m/s (Average Speed) If it takes Wiggins 4 seconds to reach 10 m/s, what distance will he have travelled? Distance = Average Speed x Time = 5 m/s x 4 secs = 20 metres

Non-uniform motion examples If a rocket accelerates constantly from 0 m/s to 11,000 m/s in 130 seconds. How far does it travel in this time? If the Earths atmosphere is 700,000 metres thick, is the rocket in space? Distance = Average Speed x Time

Non-uniform motion examples If a rocket accelerates constantly from 0 m/s to 11,000 m/s in 130 seconds. How far does it travel in this time? If the Earths atmosphere is 700,000 metres, is it in space? Distance = Average Speed x Time Average Speed = (0 + 11,000)/2 = 5,500 m/s Distance = 5,500 m/s x 130 secs = 715, 000 metres

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