Big question: how do the gears of a bicycle change how fast the wheel turns?
Make a prediction
The chainring has 42 teeth. The back sprocket has 14 teeth.
For ONE turn of the pedals, how many times does the back wheel turn?
Count and time the turns
Start pedalling. Time 10 turns of the wheel, then record.
Wheel turns0
Pedal turns0
Stopwatch
Recorded readings
0 readings
| No. | Front T | Back T | Pedal rev/min | r m | Turns N | Time t s | ω rad/s | v m/s |
|---|
Leave ω and v empty. Work them out on your results sheet.
Explain the speeds
Angular velocity ω = 2πN ÷ t. Rim speed v = ω × r. Wheel turns per pedal turn = front teeth ÷ back teeth.
Worked solution (7 steps)
Check yourself
A point on the rim and a point near the hub turn together. Which moves faster?
Gear challenge
Change the gears and the pedal speed, then press Check my set-up.
Wheel turns per pedal turn
Rim speed now
Score: 0 / 3
Big question: why does a big drill need a slower spindle speed than a small drill?
Make a prediction
The spindle turns at 800 rev/min in both cases.
Which drill's cutting edge moves faster: a 6 mm drill or a 12 mm drill?
Read the drill set-up
Choose a drill and a belt position. The spindle speed is on the speed plate.
Drill diameter D
Spindle speed n
Recorded set-ups
0 readings
| No. | D mm | n rev/min | v m/s | v m/min |
|---|
Explain the cutting speed
Cutting speed v = π × D × n ÷ 60, with D in metres and n in rev/min.
Worked solution (7 steps)
Check yourself
You change from a 6 mm drill to a 12 mm drill. To keep the same cutting speed, the spindle speed should…
Choose the right speed
Mild steel with a high-speed-steel drill needs a cutting speed of about 0.35 to 0.55 m/s.
Score: 0 / 3