Wednesday activities
Welcome to Wednesday of Science Week!
It was SO lovely to see everyone's gorgeous faces and speak with everyone in Google Meets yesterday. Your science costumes were amazing, thank you for the time and effort you put into dressing up! I hope you enjoyed seeing my watermelon implode in 'The Big Watermelon Experiment'! How amazing was it!!
Today we have a range of experiments using eggs to test density and centre of gravity. Please get an adult's permission to use the eggs (they sure do make a BIG mess when they accidentally break!) and to help you hard boil one for the experiments. We are also looking at forces and tension by building a simple catapult. Please be safe when using it!
Equipment needed for various physics experiments today:
eggs - hard boiled and fresh
jug of water
various objects to test floating and sinking
table salt
soft drink can
icypole sticks
rubber bands
plastic spoon
various objects to launch in catapult
Can a fresh egg float in water?
Ordinarily a fresh egg is denser than water - it has more matter packed into its volume - so it will sink to the bottom if placed in a glass of water. Eggs will only float if they are rotten as when they go off they produce a disgustingly smelly gas inside the shell which, if the shell gets broken, releases this horrible rotten egg gas!!! This gas makes the egg less dense than the water so the egg will float. Definitely don't want to crack that egg! So, an easy test to see if an egg is okay to eat is to place it in water before cracking it. If it sinks then carry on! If it floats then get rid of it in the rubbish bin very, very carefully, making sure you don't break it!!
BUT.... is it possible to make a fresh egg float in water? It is if you change the DENSITY of the WATER. If you make the water more dense than the egg, the 'good' egg will float! "How do I change the density of the water" you may ask? Well, watch my video to see.... or should I say sea....?
2. Using the centre of gravity
Gravity is a FORCE which pulls us towards the centre of the planet. As our planet is solid, we can't be pulled INTO the planet so the force of gravity keeps us on the surface of the planet. When we jump in the air, we use our ENERGY to push off the surface, but we will always land again as gravity acts on us and pulls us back down.
The centre of gravity is the point where the mass (or weight) of an object is even on all sides. For an evenly shaped object, like a ball or ruler, the centre of gravity would be at the middle of the object. See if you can balance a ruler on one finger. Once you find the balance point for the ruler, you have found its centre of gravity. Same goes for spinning a basketball or netball on your finger. If you can spin a ball on your finger, you are using the centre of the ball's gravity to help it balance on your finger.
We can use the centre of gravity to test whether an egg is hard boiled or uncooked by spinning them on a flat surface. The liquid centre of the uncooked egg keeps moving around, causing the egg to wobble rather than spin smoothly. The hard boiled egg which is solid inside, has a stable centre of gravity and will spin far faster and for far longer than the fresh egg. So if you're unsure whether the eggs in the fridge are hardboiled or uncooked, just spin them to test!
Also, I wonder if you can use the centre of gravity to balance a soft drink can on its edge?
3. Making a catapult
This is one version of a catapult using icypole sticks. There are many different versions but this one was very simple in design. When the spoon is pushed down it bends, creating stored potential energy. When the spoon gets released, the opposite end of the spoon pulls it back into shape, releasing the stored potential energy and turning it into kinetic or movement energy. This causes the object on the end of the spoon to be flung into the air with the force created!
Please be safe if making and using the catapult.
