Science Experiments

Archive for February, 2008

Question: physical science questions HELPPP?

Why does momentum not appear to be conserved during a collision?

A. Energy such as heat and magnetism prevent momentum transfer.
B. Friction between colliding objects reduces momentum transfer.
C. Objects are insulated against full transfer of momentum.
D. Momentum is only conserved completely in controlled experiments.

What happens to the momenta of two objects which collide and then stick together?

A. The momenta of the objects remain separate and the objects spin unpredictably.
B. If the momenta are different, heat is given off.
C. If the momenta are equal, the objects will slow down.
D. The momenta of the objects combine and the combined momentum vectors are added together to get one resulting momentum.

What is the impulse acting upon an object if a force of 25 N is applied for 10 seconds? Use Δρ = force/time.

A. 2.5 kg·m/s
B. 250 kg·m/s
C. 15 kg·m/s
D. 35 kg·m/s

Answer: > Why does momentum not appear to be conserved during a collision?

The answer choices are poor. The correct answer is that the colliding objects are often subject to _external_ forces, such as friction against the _ground_ (friction between the objects themselves has NO EFFECT on the total momentum). None of the four answer choices really expresses this. Choice “D” is sort of correct, but it really doesn’t answer the question “Why?”

> What happens to the momenta of two objects which collide and then stick together?

D.

> What is the impulse acting upon an object if a force of 25 N is applied for 10 seconds? Use Δρ = force/time.

DO NOT use “Δρ = force/time.” That equation is incorrect. The correct equation is “Δρ = force × time.” However, I don’t see why you’d use that equation either. Instead, you should use the definition of impulse, which is:

impulse = force × time

That equation is obviously related to the “Δp” equation, but they are not exactly the same. They give you “force” and they give you “time”; so just multiply.

I give your teacher a “D” for creating one sensible question out of three. Your teacher needs to go back to school.

JC Science Experiments – Physics – 3 of 4

Question: School system is experimental?

As a college student looking back at my elementary, junior, and high school years, I question what I really learned. I feel that the school system just experiments with us, requiring us to take biology, physics, science, etc. just to experiment and test us to see what we’d like. I feel this wastes a lot of years for students and that students should choose to follow a certain path that students care to follow. This would also shave off years off a student’s education and save tax dollars.

Does anyone agree with me or have any opinions on this?

Answer: First of all, most students in college change their major at least once. You certainly don’t want to be stuck in one profession in high school. Second, believe it or not, you don’t just take them to see if you like them. Any person with a basic education should know something about science – how genetics works, evolutionary biology, which chemicals not to mix together, the law of gravity, and most importantly, how we figure those things out.

Kids School Fun and Activities (Science Games)

Learn how to make dye from natural materials. Long before artificial dyes were invested, people used natural dyes from plants and the soil to color their clothes, pottery, and other objects in their homes. You can try making some dyes for yourself.

Try out the dyes on pieces of white cloth, such as an old handkerchief or squares cut from an old sheet. Make sure the cloth is clean and dry. Do not use cloth that has been treated with fabric softeners. These chemicals may stop the dye from working.

How do you make dye using natural materials?

Boil the leaves or fruit with a little water in a pan. Simmer for about 15 minutes and allow to cool. An alternative method is to put the plant material in a bowl and cover it with boiling water. Leave the bowl for about 15 minutes. Then make a filter. Cut the top half off a plastic bottle, turn it upside down and put a coffee filter inside. Pour the liquid from the saucepan or bowl through the filter to produce a colored liquid that you can use for dyeing.

Natural dye colors

• Red – Dye color red can be derived from beetroot, cherries, and red cabbage.
• Yellow – Dye color yellow can be derived from onion skins.
• Green – Dye color green can be derived from spinach.
• Brown – Dye color brown can be derived from iodine, tea, and coffee.
• Blue – Dye color blue can be obtained by dissolving a spoonful of flour in half a cup of warm water and add one or two drops of iodine.

Tie Dye colors