Answer:
Because of the buoyant force
Explanation:
Jumping into a pool change the amount of apparent gravity acting on a person.
Normally, for a person in free fall, the weight of the person is given by:
![F=mg](https://tex.z-dn.net/?f=F%3Dmg)
where m is the mass of the person and g=9.8 m/s^ is the acceleration due to gravity.
When a person is in the water, there is a buoyant force pushing the person upward. The magnitude of the buoyant force is
![B=\rho_w V g](https://tex.z-dn.net/?f=B%3D%5Crho_w%20V%20g)
where
is the density of the water
V is the volume of displaced fluid
g is the acceleration due to gravity
So the net force acting on the person is
(1)
Since V corresponds to the volume of the person, we can rewrite it as
![V=\frac{m}{\rho_p}](https://tex.z-dn.net/?f=V%3D%5Cfrac%7Bm%7D%7B%5Crho_p%7D)
where
is the density of the person. Substituting into eq.(1),
(2)
where we called
![g'=\frac{\rho_w}{\rho_p} g](https://tex.z-dn.net/?f=g%27%3D%5Cfrac%7B%5Crho_w%7D%7B%5Crho_p%7D%20g)
So we can further rewrite (2) as
![F=m(g-g')](https://tex.z-dn.net/?f=F%3Dm%28g-g%27%29)
so we see that the gravity acting on the person, g, has been modified into (g-g') due to the presence of the buoyant force.