Verification of Newton's Second Law Using a Tickertape
1 x runway, 9 x 10g masses plus holder, string, scissors, dynamics trolley, tickertape, tickertape timer, lab power supply, 2 x long wires, runway, pulley, drawimg pin or selloptape, access to a top-pan balance.
1. Set up the apparatus as shown above. Connect the tickertape timer to a 2V a.c. supply.
The slope of the runway should be adjusted so that the trolley runs at a constant speed down the slope when pushed (as judged by eye).
In this condition there is no resultant force acting on the trolley along the slope. The frictional forces slowing the trolley are balanced by a component of the the gravitational force acting on the trolley. The runway is now said to be ‘friction compensated’.
2. Measure the mass, m of the trolley.
3. Cut a length of tickertape (about 1m), attach to the trolley.
4. Hang a mass holder, as shown. This has a mass of 10g and therefore pulls the trolley with a force of 0.098N down the slope. With the tickertape timer running allow the trolley to be pulled down the slope.
CATCH THE TROLLEY BEFORE IT FALLS OFF THE END OF THE RUNWAY!
5. Repeat the above for pulling forces of 0.196N (20g), 0.294N (30g), 0.392N (40g) & 0.490N (50g).
6. Use the equation a = F/m to calculate the expected acceleration (in m/s2) of the trolley in each of the above five cases.
7. Use the tickertapes to determine the actual accelerations (see below).
8. Compare and comment on how your results from stage 7 compare with the calculations made at stage 6.
Calculating acceleration from tickertape
Locate the starting point (where the dots are merged).
Measure a lengthof about 30cm along the tickertape from the starting point, checking that the dots are always increasing in distance apart.
Count the numberof dot-to-dot intervals over this length. Each interval represents a time of 0.02 second. Now calculate the time taken for the trolley to accelerate over the length(ie time,seconds).
At the starting point, the velocity of the trolley will be (or very nearly) zero.
The equation of motioncan be used to find the acceleration.