Author: Cindy

Its Properties & Its Changes

By Tom DeRosa & Carolyn Reeves

Investigation #1: The Physical Side of Chemicals

Think about this. A detective collected samples of food from the table where a victim was eating when he collapsed. The detective sent them to a crime lab. A few days later, the lab called to say they had positively identified a poison in the victim’s food that was not in anyone else’s food. Have you ever wondered how someone in the crime lab could figure out what chemicals are present in food or in someone’s blood or in something else?

The Investigative Problems:

How can the physical properties of a chemical substance be used to help identify the substance?

Gather These Things:

Magnet
Iron nail
Sugar cube
Copper penny
Container of water
A piece of paraffin
Small amount of vegetable oil

Procedure & Observations

Your teacher will show you ten items. Your job is to identify one of the items on the basis of its physical properties. You should eliminate any item that doesn’t match the descriptions. These are the physical properties of the item: It is round. It is flat. You would not want to eat it. It would be hard to break. It is shiny. What is the item that has all of these properties?

Your teacher will give you some more substances to investigate, but each of these will be a pure chemical substance. They will be either an element or a compound.

Bring a magnet near each substance and observe if the magnet has an effect on it. Place each substance in a container of water and observe if it floats or sinks. Note if it is soluble (will dissolve) or insoluble (will not dissolve) in the water. Note also the color and whether it is shiny or dull. Put this information in a data table.

(sample of date table)

The Science Stuff

Physical properties are often characteristics you can see, hear, taste, smell, or feel, but may include any physical characteristics of a substance. You used some simple physical characteristics to identify one of the ten items you were first shown.

Some of the items you were shown were pure substances (like the glass), and some were a mixture of many substances (like the apple). A pure chemical substance could be either an element or a compound. (We’ll learn more about elements and compounds later.) A fragment of a pure substance would have the same properties as the whole substance. All of the basic particles in a pure substance are the same. For example, a piece of pure iron only contains particles of iron and a container of pure water only contains particles of water.

Properties such as size and shape were helpful in identifying the first items, but they are seldom considered in identifying pure chemical substances. The properties of the five pure substances listed in the chart will be present regardless of the size, shape, or amount of the substance. Scientists look for characteristics that will remain the same no matter where the chemical is found. Almost any substance can be made into a round shape, so this would not be helpful in knowing what chemical is present.

We examined physical properties of several pure substances, including the effects of a magnet, whether the substance would float or sink in water, whether the substance was soluble or insoluble in water, its color, and its shininess. There are many other properties we could have considered, such as odor, taste, density, hardness, brittleness, elasticity, melting and boiling temperatures, solubility in other liquids, conductivity of heat and electricity, and viscosity.

Making Connections

There is a huge need for methods, instruments, and trained people to identify chemical substances that are present in things. Identifying unknown chemicals is part of the study of analytical chemistry. This includes what chemical are present, their characteristics, and how much is present. There are many crime labs that hire people to help solve crimes by identifying things such as drugs, alcohol, poisons, or traces of gunpowder. Medical labs test blood and urine for the presence of many kinds of substances. Other labs help identify pollutants in the air, water, and environment. Industries must consistently monitor their products for impurities. These are only a few of the places where chemicals are analyzed.

One of the most important things any society can do is to maintain a clean source of water. During the Industrial Revolution, many factories were built next to a river so they could dump their wastes into the river. Congress eventually passed a number of laws to try and keep our water sources free of pollution. Even today, environmentalists look for better ways to prevent pesticides and other harmful chemicals from being washed into rivers and lakes after a rain.

Dig Deeper

Labs generally use both traditional methods and a variety of instruments to identify chemical substances. An instrument known as a spectroscope is often used to help analyze the chemicals in something. Do some reading about spectroscopes to find out how they work and what uses thy have.

Crime labs hire forensic scientists. What do forensic scientists do? Is there more than one kind of forensic scientist? If so, what are the different areas in which they work?

What are some of the U.S. laws that try to prevent water pollution? Do all countries have similar laws? Try to find the name of one charity whose mission is to provide clean water to people who don’t have clean water to drink.

What Did You Learn?

What are physical properties of chemical substances?
When scientists want to know what chemical substances are in an item, they seldom consider the size, shape, and amount of the item. Why is that?
Give ten examples of physical properties used by scientists to describe a chemical substance.
What is a pure chemical substance?
What are some of the things students learn about in analytical chemistry?
What are some of the main things that are don in medical labs?
How might an environmental agency use a lap that analyzes chemical substances?
Are the physical properties of pure iron the same anywhere pure iron is found?

Forces & Motion

From High-speed Jets to Wind-up Toys

By Tom DeRosa & Carolyn Reeves

Investigation #1: Wind-up Walking Toys, Speed, Time, and Distance

Think about this. Many people still consider “Bullet” Bob Hayes to be the world’s fastest runner. In the 1964 Tokyo Olympics, he was part of a 4 X 100 relay race. He was already running when he took the baton. He completed his 100 meters of the relay in 8.6 seconds. He also ran the 100-meter dash in 10.05 seconds. In this race, he started from a still position. Four years later at the Mexico City Olympics, James Hines ran an official time in the 100-meter dash that was less than 10.0 seconds for the first time ever. His record stood for several more years, but Bullet Bob’s relay race time will be a hard record to break.

These very fast runners were moving an average of about ten meters every second. Use a meter stick to mark off ten meters and make a prediction of how many meters you think you could run each second. Would you like to be able to figure out how many meters you can run in one second?

We can calculate the speed of a moving object by testing wind-up toys. How far a wind-up toy moves can be measured with a ruler. How long it takes the toy to move a certain distance can be measured with a watch. These two numbers can be used to calculate its speed.

The Investigative Problems:

How can we determine the speed and motion of a wind-up talking toy?
How can this be shown on a graph?

Gather These Things:

Walking toy
Chart
Pencil
Clock with second hand
Toothpicks
Metric ruler (with each cm divided into tenths)

Procedure & Observations

For these measurements, you will need a metric ruler where each centimeter is divided into tenths. Look carefully at the markings on the ruler. Notice there is a long line by each number. There are shorter lines following each number. The short lines are written as decimal numbers. Measure the line to the right by putting the zero mark of the ruler at the beginning of the line. The correct answer is found by writing the last whole number, a decimal, and the number of short marks following the number. The abbreviation “cm” is written after these numbers. Did you get 15.3 cm for your answer? Work with a partner. Each of you should draw two or three more lines. Measure each other’s lines. Check each other’s answers.
Lay the ruler out in front of you. Wind up the walking toy next to the ruler and measure how far it walks in ten seconds. Record. Calculate its average speed by dividing the total distance it walked in centimeters by ten seconds. Write your number answer followed by cm/s. This is read “centimeters per second.”
Measure how long it takes for the wind-up toy to walk one meter. Record. If it doesn’t make it that far, record how far it walked and the time it walked. Calculate its average speed by dividing the distance it walked by the time. The speed will be in m/s (meters per second) if it walks as far as a meter. If you measure the distance in cm, your answer will be in cm/s.
Go back to the starting point. Wind up the toy again. This time lay down a toothpick next to the ruler every time the instructor calls out a five-second interval. Record for 30 seconds. Measure the distances between toothpicks and record in the chart below.
Graph the results of distance versus time. Your teacher will show you how to put this information in the graph. Does your graph make a straight line or a curved line? Try to think of a reason for this.
Did your walking toy start out fast and then get slower until it stopped, or did it keep walking at the same speed all the way?
Race your walking toy with someone else’s. Which one was the fastest?

The Science Stuff

The motion of an object can be described by changes in its position, by its direction, and by its speed. Speed can be calculated by measuring the distance an object moves and the time it takes to move that distance. Divide the distance by the time to get the speed.

The distance traveled equals the object’s speed multiplied by the time traveled. The same units of time must be used. For example, if a toy travels 50 cm/minute and it travels fro a total of two minutes, it has traveled a total of 100 cm. The calculations would be 50 cm/min X 2 min = 100 cm. Minutes would cancel out, leaving cm as part of your answer.

Different aspects of motion can be shown on a graph. If the speed of the walking toy stayed the same, the graph line will be straight, but if your walking toy slowed down, the graph line will be a curve. Remember, the source of energy for walking toys is a wind-up spring. A tight spring may provide more energy than a loose spring.

Scientific measurements are taking in metric units. The correct abbreviation for centimeter is cm; for meter, it is m. the correct abbreviation for centimeters per second is

Cm/s; for meters per second, m/s.

1 centimeter (cm) = 1/100 meter
1 meter (m) = 100 centimeters
1 kilometer (km) = 1000 meters

Dig Deeper

See if you can use the Internet or some reference books to find the runners who have run at official speeds of ten meters per second or greater. (There won’t be many.)

Do additional research to find some more world records for swimming, skating, bicycling, or other sports.

Use the Internet or some reference books to find the top speeds of several animals. Did you find any that you could outrun? What is the difference in how humans run and how certain animals run.

(If you choose one of these projects, use a creative way to display your findings.)

Making Connections

Sometimes a highway patrol officer will stop a car for speeding, and the driver will insist that the car was traveling within the speed limit. Is it possible that the car’s speedometer is not accurate? Mile markers along the highway and a watch can tell if your car’s speedometer is accurate. To do that, have the driver hold the car’s speed at 60 miles/hour. Start timing with a watch that has a second hand as the car reaches a mile marker. Stop timing as the car reaches the next mile marker. The speedometer is accurate if the car travels one mile in 60 seconds. One mile/minute is the same as 60 miles/hour. You can also calculate the speed of your car by dividing the distance of one mile by the time it takes the car to travel from one mile marker to another.

Suppose you are traveling in a car wit the cruise control set at 65 miles per hour and your driver drives for two hours without stopping. Multiply the speed by two hours to see how many miles you have traveled in two hours, as: 65 mi/hr X 2 hr = 130 miles.

What Did You Learn?

What two things do you need to know in order to calculate speed?
What is the formula for calculating speed?
How would a line graph of the speed of a runner look when the runner goes slower and slower? Or faster and faster? Or maintains the same speed?
What are three ways in which motion can be described?
If you are riding in a car that is traveling at 60 miles per hour and you travel for three hours, how far have you traveled?
Suppose an object is traveling at a supersonic speed of 800 m/s. Write this speed using all words and no symbols.
Calculate the speed of an animal that ran 50 meters in 10 seconds. Write the number answer with the correct unit symbols.
What is the source of energy for the walking toys you used for this activity?