Mini Project-Which coin drops fastest?

Which coin drops fastest?

• Put a coin at the edge of a table.


• Put the edge of a ruler behind the coin, with the rest of the ruler extending out over the table edge at an angle.


• Put another coin on the end of the ruler that extends beyond the table edge.


• Take a second ruler and hit the first ruler (on the edge sticking out beyond the table edge) so that the first coin is thrown off the edge of the table and the second coin drops off the ruler.


• You have to listen for the results so you want to do this over a hard floor.

Which coin hits the ground first?

Science:

The coins start from the same height off the ground and are the same mass and shape, so gravity and air resistance worked on them in exactly the same way. Even if an object is thrown straight out, it will fall to the ground in exactly the same amount of time as an identical object that is dropped - the acceleration toward the ground that the objects experience as a result of gravity causes them to hit at the same time.

Mini Project Pile driver

Pile driver

• Fill a plastic jar with rice,


• carefully jab a knife into the rice five or ten times.


• The rice will settle a bit, then add more rice.


• Continue until no more rice can be added.


• Then quickly jab the knife into the rice and lift.

What happens? Why?

Science:
The rice gets more and more packed down by repeated stabs from the knife until the rice is so compact that it presses against the blade of the knife with enough force to overcome the pull of gravity on the jar.

Chem Standard 8c and 8d

The role a catalyst plays in increasing the reaction rate.

The presence of a catalyst increases the reaction rate (in both the forward and reverse reactions) by providing an alternative pathway with a lower activation energy but is chemically unchanged at the end of the reaction. When the reaction has finished, you would have exactly the same mass of catalyst as you had at the beginning.

Role of activation energy in a chemical reaction.

Activation energy is a term introduced in 1889 by the Swedish scientist Svante Arrhenius, that is defined as the energy that must be overcome in order for a chemical reaction to occur. Activation energy may also be defined as the minimum energy required to start a chemical reaction. The activation energy of a reaction is usually denoted by E_a, and given in units of kilojoules per mole.

Activation energy can be thought of as the height of the potential barrier (sometimes called the energy barrier) separating two minima of potential energy (of the reactants and products of a reaction). For a chemical reaction to proceed at a reasonable rate, there should exist an appreciable number of molecules with energy equal to or greater than the activation energy.

The sparks generated by striking steel against a flint provide the activation energy to initiate combustion in this Bunsen burner. The blue flame will sustain itself after the sparks are extinguished because the continued combustion of the flame is now energetically favorable.

mini projects and map making

This week we did more glass bending during class. We also had to make a map for the Mills Canyon Creek trip on Google maps. I also finished one of the mini projects out of the three that was due next week. My project was on the speed of the jars that roll down a binder, with one jar filled with water. Here is my map:

View Mills Creek Canyon in a larger map

Mini Project: Racing Jars!

Today on Wednesday March 5, 2010,I took two identical clear-glass jars and raced them down a binder to see which one went down the fastest, with one of the jars filled with water.
(Picture taken by Angelica Choi)

• leave one empty, and fill one with water.



• Put the lids on both jars and tighten.



• Place a large, three-ring binder on a level floor



• start the jars from the top of the "ramp" the binder forms.



• Release them and watch what happens.

Which one gets to the bottom of the ramp first? Which one rolls the farthest?

Science:

At first, the water-filled jar moves down the ramp faster than the empty one. This happens because its weight is evenly distributed throughout its volume, thanks to the water inside it. The empty jar's weight is all in the glass outside so it doesn't roll quite as fast. But as the jars begin rolling on the flat surface, the greater weight of the full jar causes friction between the jar and the floor as well as friction between the water and the inside of the jar. The full jar slows down, allowing the lighter, empty jar to take the lead!