SARAH DIX: Hello. My name is Sarah Dix. I'm a physics teacher here at Reddam House School.
Today we are going to be looking at the core practical, investigating the relationship
between force, mass, and acceleration so you can get accurate results in your experiments.
To carry out this experiment, you will need the following-- a trolley, a ramp you can
adjust, string, pulley, masses, sticky tape, card, sticky putty, the balance, two light
gates, a data logger, clamps and stands, a ruler, and a box of crumpled paper.
Firstly, prop up and adjust the slope of the ramp until the trolley just starts to move
on its own at constant velocity. Doing this will help compensate and reduce the effects
of friction.
Next you need to measure the length of the card and record the length within your results
table. Now fasten the card to the top of the trolley. Using the balance, now weigh the
combined mass of the trolley and the card, then record this in your results table.
Check that the pulley is securely fastened to the end of the ramp. Then put the trolley
at the top of the ramp. You may find it helpful to put a small amount of sticky putty by the
front wheels so that the trolley doesn't roll down. This will also act as a marker, ensuring
that you start at the same place on the ramp each time.
Now, simply set up with two light gates-- one near the top of the ramp, and one near
the bottom, making sure you adjust their positions so the card on top of the trolley passes through
each gate as it runs down the ramp. If you're unsure how to connect your light gates to
the data logger, you might need to ask for some help from your teacher.
Some schools may only have a data logger that can measure velocity only. If this is the
case, you will need to use a stop-clock to measure the time taken for the trolley to
pass between the light gates. Now you are ready to add the mass to the string and then
connect the string to the trolley.
This mass must stay constant throughout the experiment, as we only want to change one
variable at a time, which, in this case, is the mass of the trolley. It's a good idea
to move the putty to the side of the ramp, ensuring that you keep it in line with the
front wheels. And now release the trolley.
Now, record the velocity of the trolley from the data logger as it passes through each
like gate. And also, write down the time it takes for the trolley to go from one light
gate to the other. You will need to repeat this two more times. So you have three sets
of results.
You will now need to repeat the experiment several times, adding the additional mass
to the trolley each time. Make sure you add all of your data into your results table,
remembering to add the correct units to the heading.
To work out the acceleration of the trolley, you need to use this equation-- acceleration
is equal to change in velocity divided by time taken. As you repeated this experiment,
you will need to calculate the mean acceleration for each set of results. Finally, you need
to draw a scatter graph of your results.
Acceleration should be plotted along the y-axis, and the combined mass of the trolley and the
masses along the x-axis. Remember , when adding your line of best fit, it should be a smooth
curve. From this experiment, you should be able to explain the relationship between acceleration,
force, and mass, along with identifying the different types of variables.