Measurement Physics is based on measurement What is

Measurement Physics is based on measurement What is the time interval between two clicks of a counter? What is the temperature of the air? What is the speed of typhoon?

Measurement How fast? How long? How high?

We start learning physics by learning how to measure……. .

Time

Time To study motion, we need to find out how quickly an object changes its position.

Besides watches, can you think up other devices which can help us to measure and record the time and motion? Can they measure very short time intervals?

Any other method / device? For example i. by photos

Any other method / device? For example ii. by video

In the laboratory, we use a ticker-tape timer to record the motion

A ticker-tape timer -- is basically a vibrator, -- puts black dots on a tape

Experiment The ticker-tape timer

1. Set up the ticker-tape timer. 2. Put a length of paper tape through it under the carbon paper disc. 3. Slowly pull the tape for about 5 s (record with stop watch) 4. Count the number of ticks on the tape 5. Calculate the time interval for 1 tick,

For example There are 246 dots marked on the tape for 5 s. How many ticks do the timer make in 1 second? In 5 s, 245 ticks are marked. Number of ticks per second = 245 /5 = 49

A ticker-tape timer -- is basically a vibrator, -- puts black dots on a tape at the rate of 50 ticks per second, 50 Hz

A ticker-tape timer -- is basically a vibrator, -- puts black dots on a tape at the rate of 50 ticks per second, 50 Hz The error is due to 1. A miscount of the dots which are too close together 2. The reaction time in using the stop-watch.

A ticker-tape timer -- is basically a vibrator, -- puts black dots on a tape at the rate of 50 ticks per second, 50 Hz What is the time between these two adjacent dots? Time interval between two dots = 1/ 50 s = 0. 02 s

The time interval between 2 adjacent dots on the tape is called a ‘tick’ 1 tick = 0. 02 s Time interval between two dots = 1/ 50 s = 0. 02 s

By counting the dots marked on the tape, we can work out the time taken. 4 ticks! Time interval = 0. 02 s x 4 = 0. 08 s

Besides, a ticker-tape time can use to record the motion (speed).

Studying motion Analyze a ticker-tape

Constant motion Speed increasing Speed decreasing