Page 132 - Knowledge Organiser Yr8 24-25

Knowledge Base: Science 8.4 Motion Year 8
3. Distance-time Graph
3.1
What is plotted on the x axis of a distance-time graph?
Time taken (s)
3.2
What is plotted on the y axis of a distance-time graph?
Distance travelled (m)
3.3
What does a diagonal line show on a distance-time graph?
The object is moving at a constant speed.
3.4
What does a horizontal line show on a distance-time graph?
The object is stationary.
2. Measuring Speed
You conduct an experiment in which you measure the time taken to travel a distance of 20m. In the first condition you run, in the second you walk and in the third you hop. You measure the time taken to complete each condition three times. You then use your results to calculate your average speed.
2.1
What is the independent variable in this experiment?
The method of travel: running,walking or hopping.
2.2
What is the dependent variable in this experiment?
The time taken to travel 20m. Measured in seconds.
2.3
Name one thing that you would want to control in this experiment?
The distance of 20m.
2.4
Why can we discuss the precision of the results?
Because they conducted 3 trials of each condition and calculated a mean. You can then see how close each trial result is to the mean.
2.5
What is an anomaly?
A result that does not fit the trend.
3.5 How do you calculate the gradient of a line? gradient = change in the y axis ÷ change in x axis
3.6
What does the gradient of the line tell us on a distance-time graph?
The constant speed of the object for that stage of the journey.
3.7
If you have a steeper line in one section of a distance time graph, what does that show?
The object is travelling faster in that section.
3.8
Here is a distance time graph.
C B
A
a) Calculate the constant speed of the object in the first 4 seconds of the journey (section A).
b) What do you know about the motion of the object between 4-7 seconds.
c) Which part of the journey did the object travel the fastest: A, B or C and how do you know?
a) Speed = distance ÷ time Speed = 5 ÷ 4 Speed = 1.25m/s
a) The line is horizontal therefore the object must be stationary.
b) The gradient of the line is steepest in section A and therefore the object must be travelling faster than in section C.
4. Relative Motion
4.1
What is relative motion?
How fast one object is travelling compared
to another.
4.2
How do you calculate the relative speed of objects moving in the same direction?
relative speed = fastest speed – slowest speed
4.3
How do you calculate the relative speed of objects moving in different direction?
relative speed = speed of object 1 + speed of object 2
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