Observing and Recording Motion of Fluids

BACKGROUND:
Motion in fluids is different from motion in solids. Gravity affects solids much more than fluids. However fluids are influenced by density and pressure. For examples, ask students how a straw works? Many of the students will say that you "suck" up the soda. However, the pressure in the straw is reduced and allows the weight of the atmosphere to press the liquid up into the straw. Would a student be able to use a straw in an open container in space? No, there is no atmospheric pressure, so containers have to be sealed to work. It is difficult for students to realize that pressure will cause such movement.

The principles that influence motion in fluids also influence motion of gases in the same way.
PROCEDURE:

This goal of this lab is to see if students remember the principles that you demonstrated in the PRE LAB. Students do not have to know the physics behind the principle, just to begin to recognize these principles all around us. These toys are not the only items that show fluids moving. You may want to exchange other items, if you do not have these available.


The following helps guide students inquiry using each of the items listed in materials.

TOUR OF BUBBLE - Have the students flip the tube over when the bubbles stop moving. As the students are doing the lab make sure they observe the shape of bubbles and how they move. Air is trapped on one side and when you flip it over the air, since it is lighter will rise through the denser liquid. This illustrates Archimedes's principle, which explains why bubbles rise.
SAND TIMER - Have the students flip the tube over when the timer inside reaches the top. Students should try to decide if the sand in the timer has anything to do with the movement. It does not, the timer is actually just a bubble, which illustrates Archimedes' principle as in the Tour of Bubbles.

DENSITY TIMER - Have the students watch one liquid displace the other liquid as you keep flipping this density timer. One liquid is heavier than the other and falls through, but it also displaces the less dense liquid and pushes it upward. This is Pascal's principle in action. The stream of liquid continues as drops when all the air is pushed up. As the air is pushed up it makes it look like a volcano, because the air is the least dense of all so it moves quickly through both liquids.

WAVE MACHINE - similar to Density Timer

TORNADO TUBE - You must get two containers (plastic liters from soda). Fill one of the bottles ½ to 3/4 full of water. You may want to put a little bleach to prevent bacterial build up and food coloring (to look better). Demonstrate to the students a few times how to swirl the top of the bottom and the water will rush down. The connection, where the two bottles are joined, increases the fluid velocity. The pressure is then released once the water goes through the constriction and slows down. The vortex that pushed the liquid through the tube is maintained. This is an example of Bernoulli's principle, but this one is difficult to fully understand. Remember these exercises are to just show students different types of fluids.

TORNADO BOTTLES - This also illustrates Bernoulli's principle.

GLIDER - Students should throw the glider and see what happens. Have the students take the nose piece off and have them throw it. Notice that the motion is circular without the nose cone. Bernoulli's principle is at work.

PUDDLE JUMPER - Hold the puddle jumper firmly at the back of your left palm with your right fingertips. Make sure your fingers are straight and rigid. Keep your thumbs down. Always point the puddle jumper away from yourself and others. Tilt the puddle jumper forward, away from yourself at an angle. The puddle jumper will fly in the direction the stick is pointing the propeller. Keep it pointed forward while you spin it so it flies forward when you let it go. You must spin the puddle jumper counter clockwise. Launch it with only one stroke. Always push your right hand forward. Squeeze the stick and roll it forward to spin the propeller. Keep squeezing all the way down your left hand as you spin the stick. Spread your hands apart to release the stick as you roll past your left fingertips. Lift is the force that pushes the puddle jumper upward through the air. When you spin the propeller the energy is stored as momentum by the mass or weight of the propeller. It will continue to climb higher and higher until it is overcame by the forces of friction and gravity. Bernoulli's principle contributes to the lift.

TIMES UP - Have the students turn the item and watch the particles move. The particles are lighter than the liquid. The principle is like the density timer, except one of the mediums is not liquid. The liquid is heavier than the particles and falls through, but it also displaces the less dense particles and pushes them upward. This is Pascal's principle in action.

HAND BOILER - A student should hold the hand boiler in the palm of their hand. They should hold the bottom chamber, but not squeeze it. The liquid will move upwards and looks like it is boiling, but it is not. The heat of a warm hand will affect the molecules of the liquid and make them expand. This changes the pressure in the bottom chamber. The pressure than forces the liquid to rise first and then the air that is trapped in the chamber also will rise. When the air moves into the liquid it makes it look like you are making it boil. This is an example of Pascal's principle with the air in the tube acting like a fluid. CAUTION: This toy is made of glass, students should handle with care.

PIPE - Students should blow into the pipe and try and balance the ball so it looks like it is floating. Bernoulli's principle is being demonstrated. The movement of the air (fluid movement) causes pressure to be greater under the ball and less on the top of the ball. This pressure lifts the ball.