Backup Video (Distance-time graphs and Velocity-time graphs) - Motion, Class 9, Science Video Lecture

[Music]
when we're talking about motion it can
be very useful to draw a graph if you're
moving in a straight line a graph that's
useful is a distance time graph this is
where you have distance on the y axis
and time on the x if we mark this as the
starting point and start walking at a
steady speed of 2 meters per second then
we can plot this on the graph and draw a
straight line between the points if we
decide to stop the line would be flat
then if we return to our original
position the line slopes back to the
origin of the graph you can use the
steepness of the slopes to work out your
speed if the line is very steep then
you're moving very fast but if you're
moving slowly then the graph will have a
gentler slope you can then use the
numbers on the axis to work out the
actual speed you were traveling the
equation for speed is distance over time
so all you have to do is read the
numbers if you travel 20 meters in five
seconds then your speed would be 4
meters per second if you want to work
out how fast an Apple falls to the
ground then a distance time graph won't
do because the pull of gravity causes it
to accelerate instead we can use a
velocity time graph in this case the
slope on the graph tells us that an
object is accelerated if the line is
straight then the acceleration is
constant and if it's curved the
acceleration is changing you can work
out the acceleration of an object by
dividing the change in velocity by the
time it took to fall if the graph shows
a horizontal line the object is
traveling at a constant speed when the
graph starts to slope back to the origin
it means the object is decelerating for
instance when the Apple hits the floor
the graph would show a very steep line
you can also find the distance you've
traveled by working out the area under
the graph it's as easy as working out
the areas of squares triangles and
trapeziums and hence how far you've
traveled
[Music]
you
[Music]