Science Buddies: "Ask an Expert"

My son wants to know how to adjust his aim if shooting at something in the water. For example, he's on a ship shooting at a submarine. The idea is to use a tub filled with water and shoot a "projectile" at the floor of the tub and see how much it deviates from a straight line (as it would in air). If he adjusts the angle of the shooter, he can hopefully see a trend.

Another thought was to change the shape of the projectile and see what that does to the path (sphere, cube, egg, pyramid, bullet shapes)

We're having trouble creating the hypothesis though and also the control (projectile in air?) Any ideas what this If...Then statement would be?

thanks!Rochelle

Hello rmellot,

Motion of a projectile is slowed by drag against the fluid in which it is moving. Drag forces in water will be greater than in air because of water’s higher density and viscosity. So a projectile’s velocity will be slower in water. That means you have to aim higher to hit a target in water.

The following site has a nice simulation of projectile motion:

https://phet.colorado.edu/en/simulation ... ile-motion

The simulation doesn’t include projectile motion in water but you can see the effects of drag forces in air.

A hypothesis is a statement of how you think a dependent variable will respond to changes in an independent variable. Once you’ve settled on your experiment and have identified the dependent and independent variables your hypothesis should fall into place. Information about variables and constructing a hypothesis can be found here:

https://www.sciencebuddies.org/science- ... bles.shtml

https://www.sciencebuddies.org/science- ... esis.shtml

I hope this helps. Please post again if you have more questions.

A. Norman