Evan's Space

Wonders of Physics


23 Comments

Ticker-tape Timer – Finding acceleration


The diagram shows a strip of paper tape that has been pulled under a vibrating arm by a car moving to the left. The arm is vibrating regularly, making 50 dots per second.  What was the acceleration of the car?

ticker tape

Solutions: View the video tutorial to understand where to take time interval.

The arm vibrating 50 dots per second = frequency of 50 Hz   (50 holes are produced in 1 second)

Hence, the period, T = 1/f = 1 / 50 = 0.02s     (every 0.02s, a hole is created on the tape)

To find acceleration, a, we need to find initial velocity, u,and the final velocity, v.

u = dist / time = 0.02m/0.02s = 1 m/s

v = dist / time = 0.04m/0.02s = 2 m/s

To find acceleration, we can use a = (v-u)/t , but the time, t, taken for the increase in velocity is where most students will make a mistake.

Many will take 7 intervals to calculate the t, which is wrong.

But the intervals should be 6, starting from the middle of first interval and middle of last interval.
This will give a more accurate acceleration.

Hence, t = 6 x 0.02s = 0.12s a = (v-u)/t = (2-1)/0.12 = 8.33 m/s2


1 Comment

Kinematics – Ticker Tape Timer

Many are familiar with ticker-tape timer.  The tape is attached to Car B. As Car B moves to the left, it pulls the tape with it. The tape will go through the ticker-tape timer machine. The machine is stationary and it just punches holes on the tape as the tape is pulled to the left.  It is clear that Car A is accelerating as the distance interval of the holes is getting wider.

Media_httpevantohfile_veyam

For Car B, the scenario is different. Oil is leaking from the car onto the road at fixed interval or frequency. Hence Car B is decelerating as the distance interval of oil drops becomes smaller.

Media_httpevantohfile_jvcfr

Therefore, be careful with the two scenarios and do not be confused.