Answer:
When an air particle bombards a smoke particles, the smoke particle moves to the same direction as the air particle that hit it. When another air particle hits the smoke particle, it changes its direction to that of the second air particle, and so on. This is called Brownian motion.
In a science experiment, the dependent variable is the thing that will change based on what else is happening in the experiment. The independent variable is the thing that stays the same every time.
Answer:
The data that we have is:
Initial height = 2m
Initial vertical speed: As the sister is only pushed, we can assume that we do not have initial speed in the vertical axis.
Then at the beginning, we only have potential energy, that (using the water as the zero in our axis) can be written as:
U = m*g*h
where m is the mass of your sister, g is the gravitational acceleration, and h is the initial height:
h = 2m
g = 9.8m/s^2
Now, when your sister is about to touch the water, all the potential energy has be transformed into kinetic energy:
K = (m/2)*v^2
Then we have, at that moment:
K = U
(m/2)*v^2 = m*g*h
We want to solve this for v, that is the velocity.
v = √(2*g*h) = √(2*9.8m/s^2*2m) = 6.26 m/s
So the speed at which your sister hits the water is 6.26 m/s