Our eyes can only see a certain amount of pictures per second. They are actually quite slow. This is why we cannot see objects that are moving extremely fast. In this experiment we are going to use the slowness of our eyes.
You will need
- Pens or colouring pencils to draw a picture
What to do
- From the paper cut two pieces with the same shape and size.
- Draw two different pictures on the two pieces of paper that can also go together, for example a rabbit on one piece of paper and grass on the other. You could also do a bowl of water on one piece and fish on the other one. Or a bird on one piece and a tree on the other one for the bird to sit on.
- Tape both pieces of paper on either side at the end of a pencil. The pictures need to face outside.
- Now rub the pencils between your hands as if it was a stick that you want to light a fire with.
- Look at the pictures.
- You will see both pictures combined together, for example the rabbit sitting on the grass or the fish in the bowl.
The reason this works is that our eyes are too slow to follow the fast movement of the pictures and can only see a limited amount of pictures per second.
You can also watch this experiment as a video:
When a balloon is rubbed against hair, a towel or a jumper, it gains more electrons which have a negative charge. This gives the balloon an overall negative charge. Objects with a positive charge or no overall charge like a tin can will now be attracted (= be drawn) to the balloon. We call this “static electricity”.
You will need
- Towel, jumper or your hair
- Empty soda can
- Water tap
- A smooth surface, e.g. a table
What to do
- Blow up the balloon.
- Put the empty soda can on its side on a smooth surface.
- Rub the balloon on a towel, jumper or your hair to create static electricity.
- Hold the balloon close to the side of the soda can, but do not let them touch.
- Slowly move the balloon away from the soda can along the surface.
- Observe what happens.
- Rub the balloon again on a towel, jumper or your hair.
- Open the water tap, so that only very little water is running. It should be almost dripping.
- Hold the balloon close to the water, but do not let the balloon touch the water.
- Observe what happens.
You can also watch this experiment here:
Density tells you how heavy a certain volume of a substance is. It decides which materials can float on water and which sink. For example, a rock will sink because its density is higher that the density of water. However, wood floats because its density is lower than that of water.
The same is true for liquids. Liquids with high densities sink, while liquids with lower densities float. We are going to use this to make a rainbow in a glass. Chocolate sauce has a highest density of the four liquids and will stay at the bottom. However, water has the lowest density and will, therefore, float on top.
You will need
- 1 Glass
- 1 Spoon
- Chocolate sauce
- Washing up liquid
- Red food colouring
What to do
- Start by pouring chocolate sauce into your glass until it is one quarter full.
- Use the spoon to carefully add the honey until your glass is half full. Do NOT stir!
- Now add the washing up liquid slowly and until your glass is three quarters full.
- In a separate glass mix water with red food colouring.
- Carefully add the water dropwise until your glass is full. Do NOT stir!
You can watch this experiment as a YouTube video:
Air is made from gas particles. They constantly move around at a high speed. When speeding around like this, the particles often collide with the walls of their containers. For example, the air particles in a balloon move around and hit the balloon’s walls. These collisions cause the balloon to stay inflated. We call this gas pressure.
There are two ways to affect gas pressure. One is to change the number of air particles. When you blow up a party balloon, you add more air particles to it. More gas particles hit the walls more often and the balloon’s pressure increases.
The second method to increase pressure is by raising the temperature. When it is warmer, the gas particles have more energy and move faster. If the particles move faster, they hit with the walls more often and the pressure increases. When decreasing the temperature by cooling, the gas pressure will decrease.
In this experiment we are going to look at what happens to the pressure inside a plastic bottle when you cool down the temperature.
What you will need
- 1 empty plastic bottle (a small bottle is enough, 500 ml or even smaller)
What to do
- Remove the lid and put the empty plastic bottle in the sun or on the radiator to heat up a bit.
- Close the lid tightly, so nor more air can move in or out of the bottle.
- Put the bottle in the freezer and wait for one hour.
- Collect the bottle from the freezer. What has happened to it? Take notes.
- Now observe the bottle for a couple of minutes after taking it out of the freezer.
1. What happened to the bottle in the freezer?
2. Why did this happen? Look back at the introduction to find some clues.
3. What happened to the bottle after you took it out from the freezer?
4. Why did this happen? Look back at the introduction to find some clues.
5. Why was it important to close the lid tightly before putting the bottle into the freezer?
6. How could you improve this experiment?
In a gas, the particles move around at high speed. By doing this they collide with the sides of their container and produce a force. This is the force that keeps balloons and tires inflated. We call it gas pressure.
There are two ways to increase gas pressure. The first is to add more gas particles. More gas particles can collide with the walls more often which increases the pressure. This is what happens when you blow up a balloon or pump up your bike tire. You add more air particles.
The second way to increase gas pressure is to increase the temperature. When it is warmer, gas particles gain more energy and can move around faster. At a higher speed the particles collide with the walls more often and the pressure increases.
If you reduce the temperature, the opposite happens. The gas particles move slower and collide with the walls less frequently. This decreases the gas pressure.
- What causes gas pressure?
- How can you increase gas pressure? Describe both ways.
- How can you decrease gas pressure?
- What would happen if I put a party balloon into the sun on a hot day? Why?
- What would happen if I put a party balloon in a freezer? Why?
You will need:
- Coloured sweets, for example smarties or skittles
What to do:
- Choose three colours that you want to use in your atom. Once colour for the protons, one for the neutrons and one for the electrons.
- Cut some string to make the electron shell.
- Put the sweets that represent the protons and the neutrons in the middle. The middle of the atom is called the nucleus.
- Arrange the string in a circle around the nucleus. It will form the electron shell.
- Put the sweets that represent the electrons on the electron shell (string). Make sure that the amount of protons and electrons is the same.
- Your atomic model is now complete. If you wish you can label the atom and add the charges for protons, electrons and neutrons.
You can watch this experiment on YouTube:
Radioactive radiation is dangerous because it is ionizing. This means that it has enough energy to knock electrons out of their shells and thus turn atoms into ions.
A large amount of ionizing radiation can cause radiation burns (skin burns) and radiation sickness. Small amounts of ionizing radiation can damage DNA. This is called mutation and can later lead to cancer. If mutations occur in gametes (sex cells), they can be passed on to the next generation and can cause birth defects in newborns.
Protection from radiation
We are exposed to background radiation all the time. However, the amount is too small to harm us. But people who work with radioactive materials are exposed to more radiation and need to take precautions.
There are three ways to limit the effects of ionizing radiation: keeping a distance from the source, shielding and a time limit to exposure. For example, radioactive samples are always handled with tongs to keep a distance and stored in containers with thick lead walls for shielding.
Ionizing radiation is also used in hospitals to detect and treat cancer. Patients can be exposed to small amounts of radiation during their treatment. However, this is only done if the benefits are greater than the risks.
Irradiation and contamination
Sometimes there are accidents in nuclear power stations which can lead to radioactive materials escaping to the environment. This can lead to the irradiation and contamination of plants, animals and people. It is important to understand the difference between irradiation and contamination.
Someone is irradiated if they are close to a radioactive material and exposed to its radiation. Once the person moves away the irradiation stops.
Someone is contaminated if they get particles of radioactive material on their skin or inside their body, for example by eating or breathing. This person continues to be exposed to the radiation until all the material has decayed inside their body.
Things to do
- What is ionizing radiation?
- Give four effects of ionizing radiation on the human body.
- Why is background radiation not dangerous for us?
- State three ways to protect yourself from radiation.
- Why are radioactive samples handled with tongs and kept in lead containers with thick walls?
- What is the difference between irradiation and contamination?
- In case of a nuclear accident, what is worse? Irradiation or contamination? Why?
- Do you know any examples of nuclear accidents that have happened around the world? If yes, which do you know?
In 1932 James Chadwick, a British scientist, discovered the neutron. His discovery explains how isotopes are formed. Isotopes have the same number of protons, but different numbers of neutrons.
We can also say that the atomic number is the same, but the mass numbers are different. Isotopes are the same element because their atomic number does not change.
We refer to an isotope by adding its mass number to the element’s name. The isotope in the diagram below is called carbon-12.
Carbon can occur as three different isotopes. They are called carbon-12, carbon-13 and carbon-14.
Carbon dating is used to identify the age of very old objects, for example the remains of extinct animals such as mammoths. The amount of the carbon isotope carbon-14 in an object is examined to determine its age.
Things to do
- Fill in the missing words and numbers to describe the similarities and differences between isotopes of the same element. a) Isotopes are atoms with the same number but different number. b) They have the same number of protons and electrons but different numbers of .
- Name the scientist who discovered the neutron.
- Why are isotopes the same element?
- How do we refer to isotopes?
- Name the three isotopes of carbon.
- Why is the isotope carbon-14 useful?
- Using your knowledge about isotopes, fill in the gaps in the table a, b and c.
Remember that the atomic number is the same for isotopes of the same element.