Module 2
Planning Guide

Lab 1.5
. Exercises
. Experiments
. Answers

Lesson 1.5
Lesson 1.6
Lesson 1.7
Lesson 1.8
Lab 1.5
Lab 1.6
Lab 1.7
Lab 1.8
Project 2

Physics Lab 1.5 Acceleration

Experiment 1.5.1 Measure Acceleration using a Ticker Timer

The purpose of this experiment is to illustrate the use of a tape/ticker timer in measuring speed and acceleration

Materials and Equipment

• Laboratory tape-timer – a spark timer would be best but a timer that uses the impact of a small piece of chain on carbon paper might be easier to obtain.
• Laboratory cart, toy car or skateboard
• Battery powered toy car that travels at a constant speed
• Stopwatch – or watch with stopwatch function
• Pulley that can be mounted on the edge of a table
• Weight (500g)
• String (5 meters)
• A ruler or tape measure – with mm scale.

A note about spreadsheets
A spreadsheet program can be used successfully to report the results of the main experiment in this lab. There are a number of calculations that need to be repeated and lend themselves to automation. Spreadsheets also create excellent graphs. So, if you are not familiar with spreadsheets, this lab may provide a good opportunity to learn to use spreadsheets.

Procedure

A: Calibrate the timer

1. Place the timer at one end of the table.
2. Thread a piece of paper tape about 2.5 meters long through the timer and attach it to the toy car.
3. Use masking tape to mark 2 lines across the path of the car. These should be between 1 and 2 meters apart. Measure this distance. Call this distance D.
4. Start the timer and the car and use the stopwatch to measure the time taken to cover the distance between the lines. Calculate the average speed while passing between the two lines.
5. Count the number of equally spaced dots in a length of the tape equal to D. These dots should have been made at more or less the same time that the car passed between the lines.
6. Calculate the average time between the dots.

B: Measure the acceleration of the laboratory cart

1. Mount the pulley on the edge of the table and thread the string through the pulley.
2. Attach one end of the string to the cart and the other end to the weight. The length of the string should be such that the weight is at the edge of the table while the cart is at the other end of the table.
3. Place the timer at the end of the table - opposite to the pulley.
4. Thread a piece of paper tape equal to the length of the string through the timer and attach it to the cart.
5. Hold the weight below the pulley and take up the slack in the string by moving the cart towards the timer. Ensure that there is no or as little slack as possible on tape between the cart and the timer.
6. Start the timer and allow the weight to fall. (Place a cushion on the floor below the weight)
7. Measure the distances between the dots on the tape.
8. Enter the values in the table below.
9. Calculate the rate of acceleration of the cart

C: Repeat the experiment either with different masses attached to the string or with different masses attached to the cart.

Calculations

A: Calibrate the timer:
Calculate the speed of the toy car from the time taken to cover the distance between two marks on the table. Measure the average distance between dots on the tape and estimate the average time between dots.

Assume that the distance between the lines is 1.5 meters and the time taken to cover this distance is 3.54 seconds,
the average speed is 1.5 / 3.54 = 0.424 m/s

If there are 159 dots on 1.5 m of tape:

The distance between each pair of dots is equivalent to 3.54 s / 159 = 0.0223 seconds

B: Measure acceleration of laboratory cart
The spaces between the dots on the tape increase in length with the acceleration of the laboratory cart.
The time between each pair of dots is 0.0223 seconds. Calculate the average velocity between pairs of dot
.Acceleration is the rate of increase in velocity. The rate of increase in average velocity between successive pairs of dots is a good approximation of the rate of acceleration.

Calculate the difference in velocity between successive values of the velocity. The rate of change in velocity should be more or less constant and equal to the acceleration.

Datasheet
Enter the measurements in the following datasheet and calculate the velocities and rates of acceleration between pairs of dots.

Graphs
Plot the change in distance with time, the change in velocity with time and the rate of acceleration.
The plot of distance with time should be curved with the distance between dots increasing with time.
The plot of velocity versus time should be a straight line with a constant slope.
The plot of acceleration should be horizontal with a value that is constant at the rate of acceleration.

Typical results

The following are typical results from an experiment with a timer tape.

1. A car covers a measured mile in 55 seconds. What is its average speed?
2. The time taken for a toy car to travel between two marks on a table is 3.8 seconds. If the marks are 1.5 meters apart, what is the average speed of the car between the two marks on the table?
3. A laboratory cart is attached to a strip of paper that passes through a timer as it accelerates. The timer makes dots on the strip of paper every 0.025 seconds. The distances between three successive dots are 7.4mm and 8.8mm.
   What is the average speed of the cart represented by the distance between the first two dots?
   At what rate is the cart accelerating?

Physics Lab 1.5 Measuring Acceleration

1. 1 x 60/55 = 1.09 miles per minute or 65.45 miles per hour.
2. 1.5 / 3.8 = 0.395 m/s
3. Average speed between first two dots = 7.4 mm / .025 s = 296 mm/s = 0.296 m/s
   Average speed between the next two dots = 8.8 / .025 = 352 mm/s = 0.352 m/s
   Average increase in speed in 0.025 seconds = (0.352 – 0.296) = 0.056 m/s
   0.056 m/s increase in 0.025 seconds = 2.24 m/s².

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