To understand the answer to that question, we must understand density first. Density is mass divided by volume. Volume is how many cubic units a 3-D object contains (how many cubes, that are the same size, can fit inside the object). That’s why the unit for volume is cubic.
Mass is easily confused with weight. On Earth, weight is the force of Earth’s gravity on you. Issac Newton was inspired by Kepler’s Laws of Planetary Motion to come up with his own laws of motion.
Newton’s first law says an object in motion will stay in motion unless another force acts upon it and similarly, an object at rest will stay at rest unless another force acts upon it. This is also called inertia.
Newton’s second law is a formula: Force equals mass times acceleration. And his third law states that every action has an equal and opposite reaction, which may sound familiar because it’s also part of the lyrics in Hamilton (“Washington On Your Side”).
We can use Newton’s second law, force equals mass times acceleration (F=ma) to find the weight of an object, if we know its mass and its acceleration, but this only works if the object is in free fall — which means nothing is acting on the object except gravity. (If we were measuring the force of gravity of an object [weight] on Earth, the acceleration would be 9.8 m/s2). This means we also negate air resistance. This tells us that weight and mass have some type of relationship but in the real world, where air resistance can’t simply be negated, it isn’t that defined.
The SI unit (International System for Units) for mass is kilograms (kg) and the SI unit for acceleration is meters divided by seconds squared (m/s2). So, if we multiply kg by m/s2 we would get kg*m/s2, which is technically the units for Force but we shortened it to Newtons (N).
Mass is basically defined as how much matter there is in the object. This includes what types of atoms are present in the object, how many atoms there are, and the density of those atoms. For example, a basketball and a bowling ball might have the same volume, but the bowling ball would have a higher mass. Or, a balloon that had helium in it would have a lower mass than an object made of gold that was the same size as the balloon.
There is also the Law of Conservation of Mass, which states that an object can’t gain or lose the value of its overall mass. The components of the object can rearrange themselves to have different masses, but its overall mass would remain the same.
The density of water is 1 g/mL. An object would float in water if it had a density that was less than 1 g/mL and an object would sink if it were more than 1 g/mL. Beeswax and cardboard have densities of .961 g/mL and .689 g/mL respectively, which means both should float in water. Linoleum and magnesium have densities of 1.18 g/mL and 1.738 g/mL respectively, which means they should sink.
When chemicals freeze, they become denser because their molecules pack closer together. It takes up less space than it had when it was liquid. Except, water doesn’t do that. When water freezes, it expands, which is why ice cubes float in water. But any other chemical contracts, causing its solid form to sink.
This is because water is made up of one oxygen atom and two hydrogen atoms. The oxygen atom is slightly negatively charged, and the hydrogen atoms are positively charged. This makes the water molecules want to bond with each other. (The hydrogen atoms want to bond with oxygen atoms in the other water molecules.) This is called hydrogen bonding. When water heats up, the water molecules get more energy and so they move closer to each other because they’re attracted to each other. And when water molecules lose their energy/cool down, they arrange themselves in a way that has more spaces between the molecules which is what leads to water expanding.
Vaageesha Das is a rising 10th grader at Morgantown High School. Today’s information comes from: https://earthobservatory.nasa.gov/features/OrbitsHistory/page2.php; https://www.ducksters.com/science/physics/mass_and_weight.php; http://hyperphysics.phy-astr.gsu.edu/hbase/mass.html; http://zonalandeducation.com/mstm/physics/mechanics/forces/newton/mightyFEqMA/mightyFEqMA.html; https://blog.prepscholar.com/what-is-the-density-of-water; https://examples.yourdictionary.com/examples-of-density.html; https://www.cracked.com/article_20663_5-basic-things-you-wont-believe-science-cant-explain.html; https://www.sciencefacts.net/why-does-water-expand-when-it-freezes.html.
