http://deweywayneband.com/askdewey.cfm Thu, 25 Mar 2010 00:55:00 GMT http://bandzoogle.com http://deweywayneband.com/askdewey.cfm?feature=1206837&postid=213956 That's a question that, up until about 350 years ago, people thought the answer was, &quot;a hippo of course&quot;! But today we know (and have proved) that they fall at the exact same speed. Here's why: Gravity acts on all objects the same way. The earth is so massive, that it pulls all other mass toward it. Objects with more mass are pulled toward the earth harder than objects with less mass. For instance, take a piece of paper and place a marble on it. The paper will hold the marble. Now put a bowling ball on it. The paper will tear and the ball will fall toward the ground. That's because the earth pulls harder on the bowling ball than on&nbsp;the marble. This force is what you are measuring when you step onto a scale. Too many cup cakes last week? You will be more massive, and the earth is pulling you down with more force. Now it may be counter to your intuition, but this does not translate into a faster speed of fall.&nbsp;Gravity pulls down with a force of 32 feet per second per second. That means for every foot you fall, you are traveling 32 feet/sec faster than you were the previous second. This calculation does not take your mass&nbsp;into account. It doesn't matter what your mass is, you will always fall at the same speed. So now let's look at the properties of a feather. It's small (not very massive), light weight (again&nbsp;not very massive), and has lots of surface area compared to its mass (its flat with hundreds of fibers sticking out to catch wind). If you drop it, gravity acts on it with&nbsp;32&nbsp;ft/sec2 of force. But the friction of the air that surface area puts a resistance force comparable to the gravity force. The gravity force wins, but only barely. The feather floats slowly down on a cushion of air. Now look at a hippo. It's huge (very massive), and is fairly round in shape. A round shape (spherical that is) is great for a very high mass to surface area ratio. The amount of force the air puts on a hippo as it falls is minuscule in comparison to the force put on it by gravity. The hippo will fall at close to&nbsp;32 ft/sec2. Now, let's remove the air!&nbsp;&nbsp;In a&nbsp;vacuum there will be no cushion of air to float down on. So, based on our calculations above, the feather and the hippo should fall at the same exact speed of 32ft/sec2. Want proof? Check out this video of Apollo 15 Astronaut&nbsp;Commander David Scott on the surface of the moon (a near perfect vacuum)&nbsp;conducting a demonstration: <a href="http://www.youtube.com/watch?v=5C5_dOEyAfk&amp;feature=related">http://www.youtube.com/watch?v=5C5_dOEyAfk&amp;feature=related Here's a thought experiment for you: What if you were able to squash a hippo into the shape of a feather, and then dropped it off a building. How fast would it fall in comparison to an unsquashed hippo? Yeah, that's kinda gross, but it's only a thought experiment, so imagine that the hippo will be alright after we unsquash him with our hippo-squashing/unsquashing machine. Gravity acts on all objects the same way. The earth is so massive, that it pulls all other mass toward it. Objects with more mass are pulled toward the earth harder than objects with less mass. For instance, take a piece of paper and place a marble on it. The paper will hold the marble. Now put a bowling ball on it. The paper will tear and the ball will fall toward the ground. That's because the earth pulls harder on the bowling ball than on the marble. This force is what you are measuring when you step onto a scale. Too many cup cakes last week? You will be more massive, and the earth is pulling you down with more force.
Now it may be counter to your intuition, but this does not translate into a faster speed of fall. Gravity pulls down with a force of 32 feet per second per second. That means for every foot you fall, you are traveling 32 feet/sec faster than you were the previous second. This calculation does not take your mass into account. It doesn't matter what your mass is, you will always fall at the same speed.
So now let's look at the properties of a feather. It's small (not very massive), light weight (again not very massive), and has lots of surface area compared to its mass (its flat with hundreds of fibers sticking out to catch wind). If you drop it, gravity acts on it with 32 ft/sec2 of force. But the friction of the air that surface area puts a resistance force comparable to the gravity force. The gravity force wins, but only barely. The feather floats slowly down on a cushion of air.
Now look at a hippo. It's huge (very massive), and is fairly round in shape. A round shape (spherical that is) is great for a very high mass to surface area ratio. The amount of force the air puts on a hippo as it falls is minuscule in comparison to the force put on it by gravity. The hippo will fall at close to 32 ft/sec2.
Now, let's remove the air!  In a vacuum there will be no cushion of air to float down on. So, based on our calculations above, the feather and the hippo should fall at the same exact speed of 32ft/sec2.
Want proof? Check out this video of Apollo 15 Astronaut Commander David Scott on the surface of the moon (a near perfect vacuum) conducting a demonstration:
http://www.youtube.com/watch?v=5C5_dOEyAfk&feature=related

Here's a thought experiment for you: What if you were able to squash a hippo into the shape of a feather, and then dropped it off a building. How fast would it fall in comparison to an unsquashed hippo? Yeah, that's kinda gross, but it's only a thought experiment, so imagine that the hippo will be alright after we unsquash him with our hippo-squashing/unsquashing machine.]]> Thu, 25 Mar 2010 00:55:00 GMT 17A08C172B403597860A13166B663D54 http://deweywayneband.com/askdewey.cfm?feature=1206837&postid=185910 Jeremy Bailey from Fyffe, AL: &quot;People say Hot water freezes faster than cool water. Perhaps it cools at a faster rate but It would have to reach the temp of the cool water before it could reach freezing point, right?&quot; Jeremy, you are right to question this myth. Cold water will reach&nbsp;its freezing point faster than warm water, but not much faster. Here's why. It's all about temperature difference. The bigger the difference, the faster the heat transfer. So, since hot water and the freezing air have a&nbsp;great&nbsp;temperature difference, the heat transfer is faster, but slows down as the hot water cools. The cold water will begin cooling slower, but will still reach it's freezing point before the hot water can catch up (because the hot water ain't so hot anymore is it?) Here's the equation: Delta Q is the change in heat energy transfered Delta t is the change in time (because the heat transfer rate is always changing over time) k is&nbsp;thermal conductivity (this changes&nbsp;with different materials; in our case&nbsp;the material&nbsp;is ice) A is the surface area Delta T is temperature difference (this will change over time as the water cools thus changing the Delta Q) Delta x is the distance between the points where&nbsp;these temperatures&nbsp;are measured
Jeremy, you are right to question this myth. Cold water will reach its freezing point faster than warm water, but not much faster. Here's why.
It's all about temperature difference. The bigger the difference, the faster the heat transfer. So, since hot water and the freezing air have a great temperature difference, the heat transfer is faster, but slows down as the hot water cools. The cold water will begin cooling slower, but will still reach it's freezing point before the hot water can catch up (because the hot water ain't so hot anymore is it?)

Here's the equation:

Delta Q is the change in heat energy transfered
Delta t is the change in time (because the heat transfer rate is always changing over time)
k is thermal conductivity (this changes with different materials; in our case the material is ice)
A is the surface area
Delta T is temperature difference (this will change over time as the water cools thus changing the Delta Q)
Delta x is the distance between the points where these temperatures are measured
]]> Wed, 17 Feb 2010 22:55:00 GMT 434E7ED5CA853CCA074590CFAB37A41F