This is a short but sweet and obvious once you see it! 3) If you heat a sealed pot of water, does it get heavier, lighter, or remain the same. If the weight changes, how much and why? Ignore factors like air currents created by the heat. This is strictly about the mass or weight of the pot and water. Teaser 4 has nothing to do with teaser 3. They both just happen to be weight problems. 4) On an unrelated but similar note: A hummingbird bird sits in a sealed box. If the bird starts to fly and hovers in the box, does the box get lighter, heavier, or remain the same? Why? I've heard that in the old days, truckers carrying live chickens would sometimes stir up the birds as they approached the scales for the truck to be weighted. The idea being that if the birds were in flight, the truck would weigh less and they would be charged less by the weigh station. When I was in college, a few friends and I spent an afternoon trying to perform this experiment using flies and moths, a very lightweight transparent box, and highly accurate chemistry scales. As it turns out, flies and moths won't fly if they're in a box! Damn things just sat there no matter what we did. It was frustrating but kind of funny. I remember our chem professor saying, "Welcome to real science!"
Alright, I'll try. Defining weight as what the scale reads, I think the truck drivers were correct in theory, but it probably didn't work out too well in practice. Imagine a bird hovering over a scale in one case, and the same bird resting on the scale in another case. Obviously, the scale would read differently in the two cases, and I don't see how putting a cage around the bird would change that difference at all. Now, if that cage were sealed... I don't know. The bird has to push down on the air to stay afloat, right?.. I'll guess that the higher pressure zone beneath the bird would not affect the scale the same way the body of the bird resting on the scale would. So, I'll say that the sealed hummingbird box weighs less when the bird is hovering. There's another reason the truckers are correct, but it definitely wouldn't affect what they get charged at the scale 'cause the difference would be imperceivable to the scale they're on. Defining weight as a measure of gravitational force; when the chickens, or the hummingbird, are hovering, the square of the distance between their centers of mass and that of the planet is greater, so they have to weigh less when hovering. I can't think of a reason to think the pot of water would be any different when it's hot. So, bird; yes, and water; no.
Stays same both scenarios. Hot water is lighter only because it expands and consumes more space. 1 pound of water weighs 1 pound frozen or at 200 degrees. 1 gallon of hot water will of course be lighter than one gallon of cold water, but let the hot gallon cool to the same temp as the cold gallon and you will see the hot gallon is no longer a full gallon. It should be about 4% less. As for the bird, it’s weight remains in the box. Either sitting directly on the bottom of the box or the air pressure it creates by hovering pushing down on the box.
W = M*g where W = Weight= gravitational force APPLIED TO THE SCALE M = mass Ag = acceleration of gravity on earth (if we are on earth) Ag and M=Mwater+Mpot will give the same weight heated or not. (If you want to be picky, the whole heated thing will expand and have a bigger area and thus barometric pressure on it will increase on a nanoscale and so the weight will do.) The mass of the hovering hummingbird is not applied to the scale . The scale will show Wair+Wenclosure only, until the bird dies and applies herself to the scale. (The suggested force of pushing air (it is not pushing, it is lift force and it is a function of the difference of pressures above and below a wing, but it does not matter) will be evenly distributed in all directions at a reasonable size of the enclosure and will have no effect.) I always reserve the right to be found wrong, but why is it a brain teaser?
Sorry, I didn't read Crownlines entire answer. The weight of the box does not change. Crownline nailed it. We can appeal to thermodynamics and argue that the box is a closed system. So the weight of the bird has be accounted for whether in flight or sitting. Likewise, conservation of momentum requires that the downward force created by flapping must be equal to the weight of the bird. No luck on the water problem yet. Hint: What is the best known physics equation in the world?
It seems for you the best known physics equation in the world is “It is so because I say it is so” and there is no equation for Weight in physics for you.
It sure is among the public which has no clue about physics. Unless HereWeGoAgain says it is not. Then what he says becomes the law. As to physics the rule is that when you have to calculate weight you look for the definition of weight and the equation for weight.
I had to google and he is right. Heating does add weight. Not really an amount you could measure but a weight gain none the less.
If you are talking physics, the equation, please. If your talking science, sure, as you wish. You see in physics it is very simple. You need to calculate a weight. Step1. You google the definition of weight. Step 2. You google the equation for weight. Step 3. you google definitions of each component of the equation. Step 4. you put given values (in the same system of units) in the equation. You calculate the weight. In science you need to guess and think and any guess is good as long as the majority vote for it. A box with mass 1lb is filled with water with mass 2lb and it is in free fall thrown from a plane from 10000' above the gorund. Calculate the total weight of the box with water.
They would both weight the same. As long as no material can escape the pot the same quantity of water remains inside regardless of its state. The bird's weight doesn't vanish when they fly, it is supported by the lift their wings generate in the atmosphere which then pushes down on the ground infinitesimally harder.
A box with mass 1lb with air with mass .1lb and a humming bird with mass .5lb inside is in a free fall thrown from a plane from 100' above the ground. A humming bird inside "pushes" in direction of the earth with acceleration of a free fall so it always stays in the middle of the box. Calculate the total weight of the box, bird and air before it hits the ground.
How long it will take for the wings to push all air from the sealed box down? A humming bird is sitting in a sealed box with air pressure 1atm. The bird starts hovering in the middle of the box. What is the air pressure in the box now?
Mass of the bird is 0.5lb It is hovering in the middle of the box 1'x1' a wing span is 1". The bird is 1" long. What is the lift? 3. How many CFM the bird does generate? 4. Does it generate any CFM? Let's say it generates 1CFM. 1. How long it will take for the wings to push all air from the sealed box down? You missed problem 2 : A humming bird is sitting in a sealed box with air pressure 1atm. The bird starts hovering in the middle of the box. What is the air pressure in the box now?
I am afraid I am wrong. I am trying to speak physics on a science forum. The bird sits in the box: Definition: Weight is a Force applied to a scale. Equation: F=MA Masses of the bird, air sealed in the box and the box are given to be equal and =1 unit each. ↓ = Force of the box +↓ Force of the air sealed in the box+↓Force of the bird =3 Forces, (= 3A) are applied to the scale The bird is hovering in the air: ↓ = Force of the box +↓ Force of the air sealed in the box+↓Force of the bird +↑Force of the lift applied to the bird = 2 Forces (=2A) applied to the scale (↓+↑=0) What is more 3A or 2A? I am afraid I will get no answer from people who are educated only in science and who have no clue about physical reality around them.
I didn't miss #2. Though there are areas of higher and lower pressure the average pressure is still 1 atm.
