Measuring acceleration using a double mask
When an object does not start at rest, you need to measure both the initial velocity and the final velocity to be able to calculate the acceleration. One way to to do this is to use a double mask.
A double mask is a card that is shaped like the graphic below:
The width of the two taller parts of the card are measured and the card is attached to a trolley. We then place a light gate at the bottom of the slope and release the trolley.
The light gate is connected to a device that measures the time the light is blocked when the first section of the card passes through it. We input the length of the first section and the device calculates the initial velocity (u).
It repeats the measurement for the time the second part of the card blocks the light and calculates the final velocity of the trolley as it passes through the gate (v).
The device also measures the time between the first and second card to pass through the gate. This gives us the time between the velocities (t).
We now use the following equation to calculate the acceleration: \(a=\frac{(v-u)}{t}\)
Watch this video to see the correct procedure for carrying out this investigation.