When you race, the winner is the fastest. The more speed you have, the further you go in a specific amount of time. Calculating speed is just that.
In science you measure speed in metres per second (m/s).
In-order to calculate speed you need to measure the time it takes to travel between two points.
We can use the formula bellow to calculate speed
Speed (m/s) =
Distance travelled (m)
Time taken (s)
Lets say you sprint 100m. If it takes you 20 seconds to complete the run your speed is 5m/s
5 m/s =
100 m
20 s
Try the following questions
Try and calculate the speed for the following animals. Bellow are the times for a 100 meter sprint:
Cheetah = 3 seconds
Ostrich = 5.2 seconds
Tiger = 5.5 seconds
Hyena = 5.8 seconds
Usain Bolt = 8.3 seconds
African elephant = 9 seconds
If you’ve ever seen a marathon, you’ll notice that the runners don’t always go at a constant pace Some might go hard for the first few km, then coast. While other go slow, then go hard in the final few km.
At one moment in time, the speed that a person is running is their instantaneous speed. What the speedometer reads in a car.
The average speed is the total distance / by the total time it took for the race.
When you drive down the road, you may see other cars passing you by, or you may pass other cars on the way.
This is Relative Motion. Relative motion is how fast one thing is travelling compared to another.
Try the following questions
John is running a 40 km marathon. To monitor his speed John is wearing a state of the art GPS tracking device. This Device Tracks John pace over the 40 km. Every 5 km the time restarts. The data is bellow. I.e. it took John 20 minutes to jog 25 - 30 km (5 km).
Don’t forget we measure speed in m/s. 60 seconds = 1 minute 1000 m = 1 km
Distance
5 - 10 km
10 - 15 km
15 - 20 km
20 - 25 km
25 - 30 km
30 - 35 km
35 - 40 km
Time at each interval
8 min
10 min
15 min
15 min
20 min
25 min
30 min
1. In Meters per second, what is John’s instantaneous speed at 25 - 30 km mark.
2. What is John’s average speed in m/s
3. What part of the race was john running the fastest?
4. What was John’s speed while running 10 - 15 km?
This is where it might get a little complicated.
Speed is relative. Meaning if 2 cars are moving at the same speed in the same direction their relative speed is zero.
If 2 car crash into each other, travelling at 50 km/h then the relative speed is 100 km/h.
Try these questions
1. Define the term ‘relative motion’.
2. 2 cars driving towards each other crash. One car is travelling 40 km/h while the other one is travelling at 70 km/h. What is the relative speed during the crash?
3. Two cars driving side by side. They are both travelling at 70 km/h. Car B accelerates to 80 km/h at passes the car. What is the relative speed of car B?
4. A car is travelling east at 50 km/h. On the same road another car is travelling west at 20 km/h. The cars are moving away from each other. Describe their relative motion.
Questions
Short Answer Questions
1. Define speed
2. Sam drives all around for work. He records his journeys for tax purposes. Calculate the average speed over the whole trip.
3. Copy and complete the sentence below
To calculate speed you need to know the ______ and the ______ . To calculate average speed you divide the ______ ______ by the _______ _____ . You measure speed _____ to a stationary object.
Extension
4. Every morning Charlie leaves his house (Point A) and travels 50 km to work (point C). Jason also leave his house (Point B) and drives 70 km to work (point C).
a. If Charlie travels at an average speed of 1000m/s and Jason travels at an average speed of 1500 m/s who will arrive first?
b. Jason moves houses, now he is 100 km away. There is major construction on the roads for both Charlie and Jason. Charlie travels at 20 m/s, while Jason travels an average of 27 m/s. Who will get to work first?
5. Using the speed equation, explain how a speed camera works?
Using your knowledge of ‘relative’ speed answer the question bellow
6. Train A, travelling at 70 km/h, leaves Westford heading towards Eastford, 260 km away. At the same time Train B, travelling 60 km/h leaves Eastford heading towards Westford.
How long will they take to meet?
&
How far from each city do they meet?
7. Train A, travelling at 50 km/h, leaves Jasonvile heading towards Jacksonvill, 300 km away. At the same time Train B, travelling 80 km/h leaves Jacksonvill heading towards Jasonvile.
