Fluids can exert a force on objects Buoyant Force: The upwards force on objects in a fluid is called buoyant force. Buoyancy is why ice floats in water. Imagine - when a heavy rock seems lighter if lifted while in the water rather than on land.

Buoyancy In a fluid pressure increases with depth A balloon under water More pressure at the bottom of the balloon. If you push a balloon underwater the net force comes from the different amount of pressure from the top to the bottom

Density and Buoyancy Whether an object floats or not depends on density of both the object and the fluid. An object that weighs less than the fluid will float because the buoyant force is greater than the weight of the object If the object is heavier that the fluid it will sink to the bottom.

The motion of fluid affects its pressure: Faster moving air has less pressure than slower moving air. Fast moving air over a chimney top decreases the pressure at the top of the chimney and it will pull smoke out of a chimney. Slower moving air has more pressure Slow air is not as good at clearing smoke from a chimney

Bernoulli’s Principal A Swiss Mathematician from the 1700’s. Principle says – the faster a fluid moves, the less pressure it exerts on surfaces or openings it flows over! WINGS – airplane wings are shaped to make air flowing over the top of the wing to move faster than the air flowing under the wing.

RACE CARS – a spoiler is on the back of the car and it works like an up side down, (catiwonkas), plane wing to hold the car down on the ground. PAIRIE-DOGS – their ground tunnel are well ventilated. (Pairie-Dogs must smell or they are geniuses) Air on a hill moves faster than the air on the low side, this will clear the tunnels air.

Forces can be transmitted through fluids Pascal – A French scientist who experimented with fluids in a container. Pascal’s Principal – says that when outside pressure is applied to a fluid in a container, the pressure is transmitted throughout the fluid with equal strength Example - a Car Jack – the jack lifts when pressure increases inside of the jack and is transmitted throughout the liquid in the jack.

Hydraulics Machines that use liquid to transmit or increase force are called hydraulics. The advantage of using liquid over gas is that the molecules don’t squeeze as much. Gas molecules are spread out and they tend to decrease in size when pressure is added.