Transcript Slide 1 - Planetscience

In most situations, at least two forces act on any object. The overall
effect of these forces makes it act differently. For example, if a falling
object had a large mass, but only a small force acting upwards on it,
then it would accelerate.
To work out the overall force, you either add or subtract the forces
which act in the same direction. The overall force is also called the
resultant force. If you use the formula f=ma, then f is the resultant
force.
For example, if an object had a mass of 10 and an acceleration of 5,
you would do
m x a = f ~ 5 x 10 = 15
The resultant force would be 15.
All cars and free falling objects experience terminal velocity. When
they set off, their acceleration is bigger than the resistance (which
slows them down). As the object gets faster the speed increases, and
so does the resistance. The acceleration reduces, and eventually
the acceleration and the resistance force are the same, and then
the objects acceleration can’t increase anymore. The top speed is
called the terminal velocity.
If there was no air resistance, then gravity would make all objects fall
at the same speed. This has been proved on the moon, where there
is no air. If you dropped some rocks and some feathers together, they
would both hit the ground at the same time.
However, air resistance makes things fall at different speeds, so they
all have a different terminal velocity. The terminal velocity depends
on the drag in comparison to the weight. The drag for all objects is
different, and it is determined by the objects shape and area.
A skydiver’s terminal velocity changes. When their
parachute is not open, then their area is smaller,
and they can reach a terminal velocity of about
120mph.
When the parachute is open, there is a bigger
area, so there is more air resistance. This means that
the terminal velocity is lower, and the skydiver
reaches a terminal velocity of around 15mph, so it
is safer for them to land,
The skydiver on the left has a lower
terminal velocity than the one on the
right.