Usain Bolt vs Spiro Liacos

The Shedding Light on Motion series has proven to be very popular with teachers and students partly because it deals so extensively with sport and human movement. The practical activities that accompany the series (that can all be found on our Investigating Motion page) also cover, in large part, the science of human movement. Students can analyse, for example, their own 100m sprints and Usain Bolt’s 100m sprint. Below I have compared Bolt’s running ability with my own. (You can download the prac sheets below.)

A graph showing Usain Bolt’s and my velocity during a 100-metre sprint.

Bolt can run a little bit faster than me (okay, then, a lot faster than me!), but I can reach a higher speed than he can on a bike (as long as he doesn’t also have a bike). Bikes are amazing machines! At no stage did I slow down while I was on the bike. At about the 7-second mark, I changed gears because my legs were at the limit of how fast they could pedal. The gradient of the line clearly changes when I went into a higher gear.
While running, both Bolt and I have a small drop in the upward trend of our velocity at about the 5-second mark, something I can’t account for. We also both began to slow down at about the 8-second mark. This is because humans can only work with maximal exertion for about 8 seconds before the stored supply of ATP molecules is depleted (ATP is an energy-carrying molecule that powers our cells). Our cells continuously produce ATP, but in a full-on sprint they can’t supply enough. As a result, when the stored ATP is depleted, we have to slow down. However, Bolt’s dramatic slowdown at the end of his race wasn’t just due to his energy levels. In 2008, he was so far ahead of all the other runners that he started celebrating before he even crossed the finish line!

A distance vs time graph of Usain Bolt’s and my 100-metre sprints.

If we had raced together, I probably would have lost sight of him pretty early on! When he crossed the finish line, I would have been at the 65-metre mark. On the bike, I accelerated really slowly, but at about the 70-metre mark, I would have passed my running self.

Shedding Light on Motion: Teaching a Rigorous Motion Unit with a Strong Emphasis on Sport.

We’re all familiar with motion because we all move and we see movement everywhere. However, teaching the fundamentals of the science of motion to Year 10 students has, in the past, been notoriously difficult.

Part of the problem is that knowing the language of Mathematics is essential in coming to a clear understanding of motion (and the forces that cause it). Unfortunately though, it’s a language that many students often find difficult to understand, let alone apply to real-world situations.

Another part of the problem has been trying to find engaging contexts with which to teach a Motion topic. Being told that “Sue rides her bike from her house in Pitt Street to her school…” or that “Sue swims from one end of a pool to another and then back again…” and then graphically analysing her motion isn’t necessarily all that exciting to a lot of kids.

However, making sport (and human movement in general) a major contextual focus AND a major practical component of a Motion unit can lead to significant increases in engagement since sport is so popular.

When teaching my Year 10 Motion unit, I do a number of sport-related activities that my students really enjoy.

  1. How Fast Can You Kick a Ball?

The first activity is called Calculating Throwing and Kicking Speed. In this activity, we go outside and place two cones about 1 metre apart 10 metres from a wall. I then film the students as they kick a soccer ball and then throw a cricket ball as fast as they can towards the wall from between the two cones. Back in the classroom, the students work out how fast they could kick and throw the two balls. It’s a simple matter of using the equation speed = distance/time. The distance is 10 m and the time is worked out using the video. Using Quicktime, VLC, or Windows Media Player, students scroll through the video frame by frame. The number of frames gives a measure of the time taken. For example, if the video was shot at 30 frames per second, and the ball took 15 frames to move from its initial position to the wall, then the time taken was 15/30 of a second which is 0.5 seconds.

To scroll through frame by frame using…

(a) Quicktime, simply use the forward and backward arrow keys on the keyboard

(b) VLC, click on the View tab, then on Advanced Controls, and then use the Frame by Frame button at the bottom

(c) Windows Media Player, right-click the screen, click “Enhancements”, click “Play speed settings”, and then use the arrow key in the dialog box.  I’ve been doing this activity for quite a few years now and my students always seem to enjoy it.

  1. How Fast Does Usain Bolt Run?

The next sport-related activity my students do is an analysis of the way Usain Bolt ran, in 2008, his then world-record, 100-metre sprint in a time of 9.69 seconds. The activity is called Graphing Usain Bolt’s 2008 (then) WR 100m Sprint Data. In the race, electronic sensors recorded the time it took Bolt to reach the 10-m mark, the 20-m mark and so on. Using this information, students calculate Bolt’s average speed during each 10-m interval, and they can then draw up both a distance vs time graph and a speed vs time graph. Students are often very surprised to see that towards the end of the race Bolt slowed down. The human body can perform at its maximum capacity for only about 8 seconds or so!

To draw a speed vs time graph using the original data that relates to distance, we have to assume that the average speed during each time interval was the actual speed in the middle of the time interval. It’s only an approximation, but it’s the best that we can do with the available data.

Here I have reproduced part of the data table that appears on the activity sheet. Using it, we can easily calculate that, for example, Bolt’s average speed between the 10-metre mark and the 20-metre mark was 9.80 m/s. For the purposes of drawing a speed vs time graph we simply assume that this was his actual speed at the point half way in time between the time that he passed the 10-metre mark and the time that he passed the 20-metre mark. This time, which I have called the “mid-point time”, is the average of 1.85s and 2.87s which is 2.36 seconds. Students draw a distance vs time graph (Column A vs Column B) and a velocity vs time graph (Column D vs Column E).

  1. How Fast Can You Run? (As fast as a leopard!*)

I then get my students to do a practical activity where they analyse their own 100-metre sprints. We measure out a 100-metre track, placing a cone or chalk mark at every 10-m mark. When the starter gun goes off, the students, who are positioned at each 10-m mark, all start timing and the subject sprints along the length of the track. The students record the time it takes the subject to reach each 10-metre-interval mark. I typically place two students at each 10-m mark and the average of the two times is the one recorded on paper. We then analyse the results in a similar way to the way we analysed Usain Bolt’s effort.

Choose the prac that suits you best:

Graphing Motion: the 100m Sprint: In this prac, students analyse their own 100m sprints using Displacement vs Time graphs AND Velocity vs Time graphs.

You vs Usain Bolt in a 100m Sprint: This prac looks only at Displacement vs Time graphs and asks students to compare their sprint performances with Usain Bolt’s (when he ran his 2008 then-world-record sprint).

Graphing Motion: the 100m Sprint (Displacement vs Time only): This prac is the same as the previous prac but no reference is made to Usain Bolt.

These activities are part of the Shedding Light on Motion series which is composed of videos, worksheets, practical activities, and an online text book. The series doesn’t cover the topic of motion exclusively within a sporting context, but sport is a huge part of it. Apart from the videos themselves, all the “print” resources are free for teachers and students to download and to use in their classrooms. There are more student activity sheets on our Investigating Motion page.

The photo of Usain Bolt was taken by Erik van Leeuwen

* This line is from the classic movie Gallipoli.