My graph relationship shows that the y intercept is -0.3. Normally the y intercept should be close to zero. What factors affect the y intercept to be at -0.3?

Hi Luo,

Can you give me any more detail on your experiment? You would expect to have a y-intercept of zero in some experiments, but not all.

Assuming your experiment should have had a y-intercept of zero, any errors or inaccuracy in your raw data could lead to a different y-intercept. It could also simply stem from how carefully you have drawn your line of best fit (if drawing your graph by hand).

The experiment is the trolley travelling down the ramp.

Kia ora Luo,

Thank you for your response. There are a few different variations of that experiment. I would need to know your independent and dependent variables to give you more specific advice.

You might find this video useful. It details a similar experiment in which a marble is rolled different distances down a ramp. This link takes you to plotting the straight line graph and some discussion about the y-intercept.

Best wishes for your work.

Thank you so much. My independent variable is the distance (m) the trolley travelled.

My dependent variable is the time taken for the trolley to travel (s).

My controlled variable is the angle of the ramp. The angle of the ramp is at 3.85 degrees.

With such a low angle you should be able to accurately measure the time for some fairly small distances. As you measure shorter distances, you should find the y-intercept will tend closer and closer to zero. You may also use logic to add a point to the origin (0,0) - although if you do so, I would recommend discussing this clearly in your work. Adding a (0,0) point may still leave you with an unusual y-intercept, depending on the rest of your data points.

If this is a practice assessment, and you wanted to upload an image of your graph I would be happy to comment on it.