# Ch. 13 Elliott Physical Science

## 15 terms

### pressure

the result of a force distributed over an area

### pascal

the SI unit for pressure; very small

### fluid

a substance that assumes the shape of its container

### Pascal's principle

a change in pressure at any point in the fluid is transmitted equally and unchanged in all directions throughout the fluid

### how does pressure in fluids vary with depth and altitude?

air pressure decreases as the altitude increases

### hydraulic system

a device that uses pressurized fluid acting on pistons of different sizes to change a force

### Bernoulli's principle

as the speed of a fluid increases, the pressure within the fluid decreases; ex: spray bottles. shower curtain sucking in, airplane wing

### how do wings produce lift?

the air traveling over the top of the wings moves faster than the air passing underneath, creating an upward force known as lift

### buoyancy

the ability of a fluid to to exert an upward force on an object placed in it

### buoyant force

when an object in water is easier to lift, it is because the water is exerting an upward force, or buoyant force

### Archimede's principle

the buoyant force on an object is equal to the weight of the fluid displaced by the object

### how is density related to buoyancy?

if an object is less dense than the fluid its in, it will float; if the object is more dense, it will sink

### how is an object suspended in water?

when the buoyant force is equal to weight, the object floats

### why does a Cartesian Diver sink?

when pressure is exerted on the liquid, the air in the diver compresses and therefore the entire diver becomes denser than the liquid around it -> it sinks

### why does a curveball curve?

with the top or side spin on the ball, one side is receiving resistance more than another; the side receiving the resistance creates a high pressure system, and the other side a low pressure system; pressure moves form high to low (side to side), creating the curve