Common Misconceptions
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The majority of misconceptions occur due to the lack of acknowledgement of frictional forces, which include air resistance. In our world, it is very difficult to do anything without encountering frictional forces. Therefore to keep objects in motion we generally need to exert constant force. However, this is due to the opposing frictional force.
Showing the motion of an object with no initial velocity and a set force applied to it on ice and the same object and set up but on any other surface than ice. The students would then be asked why the distance travelled on ice is much grater than the other surface. |
One episode of The Simpsons is responsible for the common misconception that toilet water rotates differently depending whether it is located on the northern or southern hemisphere. It is true that large slow moving masses of mediums, such as water and air, rotate clockwise of counter clockwise depending on the absolute latitude and whether they lie on the northern or southern hemisphere. This is due to the rotation of the earth, commonly known as the Coriolis Effect. However, the rotation of the earth doesn’t impact the rotation of toilet water any more than it does the rotation of a CD. The shape of the toilet bowl dictates which way the water will rotate.
An easy way to clear this misconception is to have the class complete a project where they design two relatively small bowls out of putty or another material that is easy to work with. The bowls need to be almost undistinguishable visually, however when water is poured in the bowls one will rotate the water counterclockwise and the other clockwise. |
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Another common misconception is that a penny dropped from the Empire State Building would have the force necessary to crack a human skull. However, due to the frictional force of air (air resistance) objects have a terminal velocity. Meaning that in a free fall, there is a limit to their velocity. Once the force of air resistance equals the force of gravity, terminal velocity is reached. In the case of a penny, its terminal velocity is 30-50 miles per hour. Given that the mass of a penny is very small, the force of a penny travelling at its terminal velocity isn’t enough to crack a human skull. Yes, it would hurt, but it wouldn’t kill you.
To clear this misconception a simple demonstration can be shown. Simply dropping any object at the same time as dropping a feather will show that some object reach terminal velocity way faster than other. This demonstration can even lead to a lesson on aero dynamics and the design of cars through the years, particularly racing cars. More misconceptions can be found at http://www.physics.montana.edu/physed/misconceptions/ |