# 5. Measuring Acceleration

# Success Criteria

Your learning has been successful if you can do the following:

Define acceleration and its units.

Calculate acceleration from speed and time measurements.

# Vocabulary

Learn these so you can communicate this concept well.

Average speed: Calculated by the total distance travelled divided by the total time taken for the journey.

Gradient / slope: How steep a line on a graph is.

Speed: How fast an object is moving.

Velocity: Similar to speed, but also tells us the direction in which an object is moving. It includes both speed and direction of motion.

Do Now:

Collect and complete this small 'Do Now'. Then glue into your SciPAD page 11. Use your commonsense when glueing - don't glue straight on-top of words!

Find some space on page 15 of your PESS1.2 SciPAD,

and answer the following questions:

What does each letter in CUTLASS stand for?

## The Speedometer

Speedometers measure the instantaneous speed of a vehicle at any given moment. With it, you can measure the initial velocity and final velocity of the vehicle to calculate the change in velocity.

You would need to know the time interval between the initial and final speed measurements in order to be able to calculate the acceleration, using the following equation:

Note: This change from initial speed to final speed is due to acceleration!

## The Ticker Timer

A TICKER-TIMER can be used to study short and fast motion of small objects like a trolley or a toy car. When you switch on the ticker-timer, it makes a certain number of dots in a certain period of time. This is usually marked on the timer as its frequency.

The frequency of most ticker-timers is 50 Hz. This means these ticker-timers can make 50 dots in one second. So when using a ticker-timer, time is a known quantity.

The diagram below shows how ticker timers work:

The ticker-tape obtained can also be used for describing the motion of the object.

Evenly spaced dots means constant speed.

If the space between dots is widening progressively, then the object is accelerating.

If the space between dots is decreasing progressively, then the object is slowing down or decelerating.

### Worked Example 1:

Below is a middle section of ticker-tape that recorded the motion of a trolley.

### Worked Example 2:

In the ticker timer tape below, the velocity has been calculated for four time intervals. The data can be shown in a table.

# Tasks & Homework

## Task 1: PESS1.2 SciPAD

## Page 14 - Calculating Speed from a Distance-Time Graph

## Page 15 - New Zealand Secondary Schools Rally Team

## Practical:

Let's make our own human body ticker timer! Click on this online metronome and set it to 240 BPM (beats per minute).

Convert beats per minute to beats per second by dividing by 60.

240 beats per minute = 4 beats per second

Therefore, the time between each dot (beat) is one fourth of a second, or 0.25 s.