Katie Flanagan- Teacher at Alice C. Stelle Middle School
Density, Mass, Volume
Standards 8th Grade- Standard 1: The velocity of an object is the rate of change of its position 8th Grade- Standard 8.a: Students know density is mass per unit volume 8th Grade- Standard 8.c: Students know the buoyant force on an object in a fluid is an upward force equal to the weight of the fluid the object has displaced.
Materials needed Making a Bottle Accelerometer: 2 liter soda bottle Water Thumb Tack 20 cm length of string 1 cork small enough to fit through the neck of the bottle
Procedure Start with the string and connect it to the cork using the thumb tack.
Take the other end of the string and you have two choices. You may attach that end to the cap of the bottle, or just hand it outside the bottle when you put the cap on.
Fill the bottle with water
Put the cork inside the bottle and put the cap on the bottle
Turn the bottle upside down and you have a homemade accelerometer
ExplanationThe accelerometer works by showing the direction of acceleration. When you move the bottle forward the cork will also go forward, when you move the bottle backwards, the cork will also go backward, and so on.
This may be opposite then you would expect, but this is how it works. The cork is less dense the water inside the bottle. According to Newton's first law of motion, both the water and the cork want to remain at rest as long as possible, but because the water is more dense it is harder to move. Therefore, the cork will move in the direction the bottle is moving first and the water will stay at the back of the bottle. The cork will then appear to be pointing in the direction of acceleration.
Answer: The cork would stay on the inside edge of the bottle because the more dense water would move to the outside.
- According to the principles explained, what would happen to the cork if you spun the bottle around in a circle?
Answer: The demonstration would not work at all. The chalk is more dense then the water and therefore the chalk would not float to the top of the bottle.
- The density of fresh water is about 1000 kg/m(cubed). The density of the cork is about 240 kg/m(cubed). What would happen if you replaced the cork with a piece of chalk (density 2499 kg/m(cubed))? Would your demonstration still work?
Answer: The foam in the seat is less dense then you are, therefore, when the car stops suddenly, the more dense object (you) go to the back, while the less dense object (the seat) want to go to the front, although it can not go through you like the cork can in the water.
- How can you use this principle to describe the feeling you get in a car when the driver brakes quickly and it feels like the seat behind you is pushing against you?
Everyday examples of the principles illustrated
There are a ton of examples of accelerometers being used in everyday life.
- When you tilt your iPhone sideways, the accelerometer turns the page for you so
your screen is always up and down
- Washing machines use accelerometers to make sure the load is balanced
- An accelerometer could protect against a stolen car due to towing it away by
including an accelerometer in your car alarm
- Neuromuscular Stimulator- when walking, the forefoot is normally raised when moving the leg forward, and then lowered when moving the leg backward. The accelerometer is worn somewhere on the lower leg or foot, where it senses the position of the leg. The appropriate muscles are then electronically stimulated to flex the foot as required.
- It was used for high level swimming athletes to determine proper positioning in their forehand stroke.
- Package monitoring- By including an accelerometer in your package, you could determine the exact moment your package was damaged in transit based on the movement of the package.
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