 No Brain Too Small  PHYSICS 
Physics 90935:
Carry out a practical investigation that leads to a linear mathematical relationship, with direction
Plot this data as a line graph. Put drop height on the x-axis and rebound height on the y-axis.
Drop height H
(cm)
Average rebound height B
(cm)
20
13
40
25
60
33
80
55
100
64
120
80
140
95
160
106
Draw a line of best fit through the 8 points.
Calculate the gradient.
What are the units of the gradient? Does this gradient have units? Why/why not?
H
B
To find the mathematical relationship between the height a ball is dropped
115
from, H, and the rebound height, B.
110
105
100
95
90
Average rebound height, B (cm)
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
0
10
20
30
40
50
60
70
80
90
100
Drop Height, H (cm)
110
120
130
140
150
160
170
180
115
110
105
100
95
90
Average rebound height, B (cm)
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
0
10
20
30
40
50
60
70
80
90
100
Drop Height, H (cm)
110
120
130
140
150
160
170
180
115
110
No
105
No! Don't do "join the dots". Instead
100
draw a line of best fit.
95
90
AND make sure the line doesn't
Average rebound height, B (cm)
85
80
extend past 20 (first bit of data) and
75
160 cm (last bit of data)
70
65
60
55
50
45
40
35
30
25
20
15
10
No
5
0
0
10
20
30
40
50
60
70
80
90
100
Drop Height, H (cm)
110
120
130
140
150
160
170
180
115
110
105
100
Gradient = 65 / 95 = …………..
95
90
Since the units are cm/cm the
Average rebound height, B (cm)
85
80
rise =
100 - 35
= 65 cm
answer here has NO units!
75
70
65
60
55
50
45
40
35
30
25
run =
150 - 55
= 95 cm
20
15
10
5
0
0
10
20
30
40
50 55
60
70
80
90
100
Drop Height, H (cm)
110
120
130
140
150
160
170
180
Draw a straight line of best fit with a ruler, trying to get as many points above the line as below – and leaving out any really obvious outliers (anomalous
results). Select 2 points on the graph that fall on points on the graph paper those are easy to read.
•
•
•
Calculate the rise.
Calculate the run.
Calculate the gradient; rise ÷ run.
State the mathematical equation of the relationship between the independent and dependent variables.
The gradient of a straight line is given by the equation y = mx + c, where m is the gradient. (c is the intercept but we are not interested in this for this AS)
Don’t use y and x but instead substitute the labels for the variables, here B and H.
y= m x
B = 0.68 H
Accuracy improving:
•
•
Line up eye with ball and measuring device to reduce parallax errors.
Difficult to estimate the maximum height a moving tennis ball rebounds to so do lots of measurements.
Independent variable range:
•
•
Minimum dropping height was <insert relevant height> because a dropping height less than this gave too small a rebound height that could not be
measured.
Maximum dropping height was <insert relevant height> because too difficult to do accurately in a science lab.
Controlled variable:
•
•
Same tennis ball used each time because different balls could bounce by different amounts.
Ball dropped on to same surface (carpet square) as balls could bounce by different amounts on different surfaces.
Difficulties / issues:
•
Rebound height very difficult to measure as ball only stops momentarily before falling again.