Physics

BL1993

When drawing graphs which go straight throguh the origin. Is it acceptable to take the point (0,0) when calculating the slope of the graph. My teacher has warned us against doing that because he says it is experiemntally wrong and we will lose marks but I do not understand as (0,0) is on the graph. For example, if you had a graph of distance versus time, in zero seconds, a body will move zero metres which is technically right. Can anyone clarify this?

shefellover93

BL1993 wrote: »

When drawing graphs which go straight throguh the origin. Is it acceptable to take the point (0,0) when calculating the slope of the graph. My teacher has warned us against doing that because he says it is experiemntally wrong and we will lose marks but I do not understand as (0,0) is on the graph. For example, if you had a graph of distance versus time, in zero seconds, a body will move zero metres which is technically right. Can anyone clarify this?

I always take a point between the origin and first point, and between the last two points (Usually one that lines up to make nice round numbers on my graph!) The origin isn't correct as the units are different but yer taking the same points/values. That's what we were told

irish_man

BL1993 wrote: »

When drawing graphs which go straight throguh the origin. Is it acceptable to take the point (0,0) when calculating the slope of the graph. My teacher has warned us against doing that because he says it is experiemntally wrong and we will lose marks but I do not understand as (0,0) is on the graph. For example, if you had a graph of distance versus time, in zero seconds, a body will move zero metres which is technically right. Can anyone clarify this?

What your doing is correct but it mightn't get you the most accurate slope. The correctors are given a "buffer zone" (so to speak) of the correct answer. For example for an acceleration due to gravity question the answer is, lets say, 9.8, but the correctors are allowed give full marks to any answer from 9.4 to 10. (due to different values of slope etc.) By taking the point (0,0) as one of your points you are lowering your accuracy and more likely to get an answer outside the 9.4-10 buffer zone and then you lose marks.

desertstorm

I'd recommend to any student to get familiar with how marking schemes work, you can get them from the same place you get the past papers

Eathrin

irish_man wrote: »

What your doing is correct but it mightn't get you the most accurate slope. The correctors are given a "buffer zone" (so to speak) of the correct answer. For example for an acceleration due to gravity question the answer is, lets say, 9.8, but the correctors are allowed give full marks to any answer from 9.4 to 10. (due to different values of slope etc.) By taking the point (0,0) as one of your points you are lowering your accuracy and more likely to get an answer outside the 9.4-10 buffer zone and then you lose marks.

If you are taking points from your graph accurately, using the origin should make absolutely no difference to the slope as it is in fact a straight line which has been drawn. You are required to draw through (0,0) so this is always going to be on the line.
But I am curious too, as to whether it is acceptable in the workings to essentially take one point and divide the x value into the y to get the slope.

BL1993

Cian A wrote: »

If you are taking points from your graph accurately, using the origin should make absolutely no difference to the slope as it is in fact a straight line which has been drawn. You are required to draw through (0,0) so this is always going to be on the line.
But I am curious too, as to whether it is acceptable in the workings to essentially take one point and divide the x value into the y to get the slope.

This is what I was thinking too when I read this post. I mean, if you took 1 point correctly and another one incorrectly, your slope will be more inaccurate than if you took a correct point and (0,0), which is technically a correct point because it is on the line making your slope more accurate.

Mr Teacha

The line of best fit does not have to go through the origin. The line of best fit is just he line that fits most points and so does not necessarily have to go through origin (even though the origin is definitely one of the points)