Reading Motion

ready

The trap

Not a Picture

The upper channel is a distance in metres — either how far you have come down the road, or how far you are from the car ahead. Either way it is a distance against time, and never a height.

A negative gap does not mean you are going backwards. It means you are ahead. Sign is direction, never speed.

Nothing on this screen is ever a picture of the route. The car only ever moves along one line, and the upper axis counts metres along it.

A trace that rises and falls did not go over anything.

Here the hill means you lost ground, then took it back. The peak is the instant both cars are doing exactly the same speed — the channel below — how fast the gap is changing — passes through zero at that moment.

Here the peaks are the straights and the dips are the corners. The circuit is flat; the trace would look the same if it were carved into a hillside or laid on a salt pan.

Try these

Your own data

Drive It

These three traces are a record of what you do with the pedals, on a flat road. Nothing here is a picture of anything.

A speed trace that climbs is a car speeding up, not a car going uphill. You drew it yourself, on a road with no hills in it.

Make your speed trace lie on top of the target.

Press and hold Accelerate or Brake below — or W/↑ and S/↓ on a keyboard, or drag the two pedal bars. From rest, the brake pedal becomes reverse. The car has the same engine, drag and braking limits as every other channel in this instrument.

Target

Match to target

The hard part

Slope or Height

Asked for acceleration, most students read the height of the speed trace. Asked for speed, many read the height of the distance trace. Both answers are the gradient.

Full throttle and zero acceleration at the same instant. Fast and speeding up are different questions, and this is the moment that proves it.

Height is how fast. Slope is how fast that is changing.

Drag the point along the distance trace. Its gradient — rise over run — is the speed at that instant, and it is the height of the speed trace directly below.

Then watch the end of the straight. The speed trace is as high as it ever gets, the throttle is flat on the floor, and the acceleration has fallen to a few hundredths of a g — almost everything the engine gives is going into beating the drag, and it will never quite reach zero.

The hidden one

The Area

How far the car has travelled is written nowhere on a speed trace. It is the area underneath it — and that is exactly how a car's distance channel is computed from wheel speed.

How much the gap has moved is written nowhere on a gap-rate trace. It is the area underneath it — positive while the cars separate, negative while they close.

The shaded area is the distance.

Below the axis the area counts as negative, which is precisely where displacement and ground covered part company.

Try these

All channels

Trace Stack

One lap, five records of it. Drag any node on the speed trace and watch every other channel answer.

Each channel is the gradient of the one above and the area of the one below.

Distance → speed → acceleration going down, by taking gradients. Acceleration → speed → distance going up, by taking areas. That is the whole of kinematics in one sentence — and the whole of a telemetry screen.

Load a trace

The throttle and brake traces are not free channels — they are worked out from the speed trace and the car's drag, so they can never disagree with it.

Commit first

Race Engineer

Call it before the data comes up. Every other option is a mistake real students make.

All channels