Home
Site Map | Français | Contact Us

Background Information for Science Surprises

The following information should be helpful in answering some of your questions about the «Science Surprises» program material. Click on any of the questions below to access information intended to help you teach your class about chemistry, gyroscopes, cryogenics and electricity.

 

Chemistry

Gyroscopes

Cryogenics

The Van de Graaff Generator / Electricity

Chemistry

What is the pH scale?

An important branch of chemistry is acid-base chemistry. The pH scale is used to classify acids and bases of different strengths. But this is meaningless until we understand what acids and bases really are.

We often hear about the dangers of acids. For example, we have heard that acid rain kills wildlife and dissolves stone structures. Did you know that lemon juice and vinegar are also acidic solutions? Remember that lemon juice on a paper cut stings. Lemon juice is not a strong acid, but highly concentrated stronger acids used in industrial processes can be very dangerous: they will eat through clothing, skin and bone. Bases, another category of chemicals, can be just as dangerous. Household bases include ammonia and drain cleaner. Chemically, acids and bases are very different.

Any compound which yields the hydrogen ion, H+, upon dissolving in water is classified as an acid. The resultant acidic solution has certain distinct physical and chemical properties. First of all, the solution contains charged particles (due to the dissociation into ions of the solute). It will therefore conduct electricity. Acidic solutions taste sour. They release hydrogen gas upon reacting with metals such as magnesium and zinc. Acidic solutions will also change the colour of litmus paper from blue to red.

Bases yield the hydroxide ion, OH-, when dissolved in water. This creates a basic solution that is characterized by a different set of physical and chemical properties. Like acids, basic solutions will conduct electricity. However, basic solutions feel slippery or soapy to the touch. A base will change the colour of litmus paper from red to blue. Bases may also be identified by their bitter taste.

The pH scale is used to classify acids and bases of different strengths. It might help to think of a thermometer, which is a scale to classify temperatures. The pH scale is a scale from zero to fourteen. The pH values of acids are at one end of the scale, and those of bases at the other. The pH values are determined by the concentration of hydrogen ions in the solution. A neutral solution such as pure water, which is neither acidic nor basic, has a pH value of seven. Acids have pH values less than seven, while bases have pH values greater than seven.

Source: O’Connor, Davis, Haenish, MacNab, McClellan, Chemistry Experiments and Principles, D.C. Heath and Company, Toronto: 1977, (pages 290-291)

Back to menu

How does an antacid work?

When equal amounts of acidic and basic solutions of comparable strength are mixed, the ensuing reaction produces a neutral solution. This is very important to the chemistry of our stomachs. Hydrochloric acid, normally found in gastric juices, is necessary for the proper digestion of proteins in the stomach. Some patients suffer from acid indigestion, either from eating too much of certain foods or as a result of a weak lining in the stomach. In this case, an antacid (e.g., a base such as TUMS or milk of magnesia) can be administered to neutralize the excess acid in the stomach and provide relief. On the other hand, some patients suffering from hypoacidity, i.e., a lower than normal amount of hydrochloric acid in the stomach, are actually given dilute hydrochloric acid orally to overcome this deficiency.

Back to menu

How do iodine and starch react in your kitchen?

When iodine and starch are mixed, a blue complex is formed. The formation of this complex is commonly used to detect the presence of starch or iodine. Therefore, by putting iodine solution on foods that contain starch, a blue-black or brown colour will appear. This will happen with foods such as potato, rice, pasta, flour, bread and corn starch. Iodine will not produce a blue colour on foods without starch (e.g., most fresh vegetables such as cucumber and celery, sugar, salt, oil). The exact nature of the blue complex is not known.

Using iodine to test for the presence of starch is an experiment easily done at home. Iodine can be purchased in drug stores. Ask the chemist for "red tincture of iodine."

What role does starch play in the environment?

  • Starch belongs to a family of chemicals called carbohydrates. The other two types of carbohydrates are sugar and cellulose.
  • Plants use starch to store energy. The starch comes from a sugar called glucose. During the process known as photosynthesis, green plants use water, energy from sunlight and carbon dioxide from the air to produce oxygen, water and glucose. The plants then build glucose molecules either into starch for energy storage, or into cellulose, which becomes part of the plant’s structure.
  • In the human body, starch is broken down into sugar, which supplies the energy for muscular activities, and other bodily functions. This is why athletes load themselves with a high carbohydrate diet (pasta, for example) before a competition. As long as we exercise, the starch reacts with oxygen inside our body to produce energy, carbon dioxide and water. If we stop exercising, our body converts excess starch into fat.
  • Besides being a source of energy, starch is very useful in the production of liquor, and in the manufacture of glue, paper products, and cloth products.

Back to menu

Gyroscopes

What is a gyroscope?

The term "gyroscope" refers to any object mounted so that it turns very quickly around an axis of symmetry. Many different kinds of objects rotate or can be caused to rotate (e.g., a top, a bicycle wheel, a figure skater, the Earth and the other planets in the solar system, some communication and research satellites, an umbrella, an egg). All these objects display gyroscopic properties. People have used the properties of the gyroscope to invent a range of guidance and stabilization systems such as those used in aeroplanes and submarines.

Back to menu

What is special about a gyroscope?

A fundamental property of gyroscopes is gyroscopic inertia, also known as the gyroscopic effect.

The first thing we need to understand is the meaning of "inertia". This is a principle which says that all objects naturally resist any acceleration or change of direction. (For example, the occupants of a car jerk forward when the car comes to a sudden stop because the bodies, due to their inertia, are still moving forward even though the car has stopped.)

When we speak of gyroscopic inertia, we are talking about the inertia possessed by a rotating body. This is the tendency of all objects rotating around an axis to maintain a fixed orientation, or direction of spin and position; that is, if there are no forces. In other words, a rotating object tends to stay in the same position.

On Earth, spinning gyroscopes will eventually come to a stop because of air resistance and friction. However, this will not occur in an ideal environment such as Space.

Back to menu

What are some of the applications of the gyroscopic effect?

Bicycle stabilization:

It is far easier to maintain your balance on a moving bicycle than on a motionless bicycle.

We know that a rotating object tends to stay in the same position. The faster the object rotates, the greater its gyroscopic inertia and the more difficult it is to change its direction of spin and position.

For example, the faster a bicycle wheel is turning, the more gyroscopic inertia it has, the more stable the bicycle and the easier it is to maintain your balance.

Guidance and stabilization instruments (navigation instruments):

The artificial horizon used by aircraft pilots is produced by a spinning gyroscope. This instrument is extremely important to the pilot, as it shows him/her the position of the aircraft with respect to the true horizon.

In aeronautics, gyroscopes are also used in compass-bearing devices, instruments for determining direction and in equipment stabilization instruments.

Similarly, gyroscopes are used to stabilize ships and submarines

Stabilization of orbiting satellites:

Many satellites spin very quickly about their own axes. This spin gives the satellite gyroscopic inertia. The satellite then tends to maintain a fixed orientation, or direction, in space (very important for communication satellites)

.

Back to menu

How does a bicycle make use of the gyroscopic principle?

A spinning object reacts differently to an outside force than does a stationary object. If a force is applied to a freestanding object that is not rotating, the object turns in the direction of the applied force. However a rotating object does not start turning in the same direction as the force applied to it. It reacts as if a force had been applied to it at some other point. This is called precession.

Like gyroscopic inertia, precession contributes to a bicycle’s stability and ease of handling. When you are riding a bicycle, you usually try to maintain your balance directly above the point of contact with the ground, except when you want to make a turn. To turn a corner, you lean into the turn, or the bicycle will skid. You may not have realized that the reason for leaning is to produce precession in the wheel and make turning easier. The precession movement turns the bicycle in the direction you are leaning (without any need to turn the handlebars).

In other words, as you approach a right-hand turn, you lean your body and the bicycle to the right. The precession this produces automatically turns the bicycle to the right. This keeps you close to the curb and prevents skidding. You then simply return the bicycle to its former vertical position -- until the next corner!

Back to menu

How does the precession of the Earth affect its movement?

The Earth is in constant motion. There are three different types of motion that occur.

  • The Earth turns about its own axis, one revolution each day. Every 24 hours, each point on Earth travels to the side lit by the Sun (day) and to the dark side (night).
  • The Earth revolves around the Sun once every year. Because the Earth's axis of rotation is tilted, its revolution around the Sun creates the seasonal changes familiar to all Canadians.
  • The Earth also precesses just like a top or a gyroscope. The gravity of the Sun and the Moon exerts forces on the rotating Earth, which reacts by precessing around its axis of rotation.

Back to menu

What do a Telesat satellite and a figure skater have in common?

There exists a property of rotational motion that spinning figure skaters and satellites can use to their advantage:

The extension of an object turning about its own axis slows down its rotation. Likewise, the retraction of an object turning about its own axis speeds up its rotation. Although the total mass of the object is unchanged, the shape or distribution of the mass has changed, and this changes the speed of rotation.

This explains why figure skaters spin faster as they draw their arms in toward their bodies.

Other sports that make use of this phenomenon include diving and gymnastics. When an athlete extends the arms or the legs, his or her rotation is slowed down.

The Canadian aerospace industry has also made considerable use of this physical phenomenon. In the beginning of April 1991, Telesat Canada launched Anik E2, a $300 million communication satellite. However, a serious problem arose: one of the satellite’s antennae failed to open, and the situation appeared hopeless. How do you free an antenna on a satellite orbiting 37,000 km above the Earth? The engineers had a brilliant idea: make the satellite spin. It was made to rotate faster and faster until the antenna came unstuck and opened. Once the antenna was extended, the satellite’s rotation slowed down.

Back to menu

Go back to Science Surprises