Tag Archives: Newton

Newton’s Law of Cooling

One of Newton’s famous contributions to physics was his work in thermodynamics — the study of heat and energy flow. He developed a physical law that showed the proportional relationship between heat loss and the temperature difference between an object and its surroundings: Newton’s Law of Cooling. Despite its name, it can be used to show how an object will cool or heat in its surrounding.

Newton's Law of Cooling 2

It’s worth mentioning that heat and temperature are two separate — but related — values. Heat is a measurement of the total kinetic and potential energy stored in the molecules of an object, while temperature is a measurement of the average kinetic energy. Heat depends on the speed, the number, and the type of molecules. So while a cup of coffee may have a higher temperature than something like an iceberg, the iceberg is made up of so many molecules that it has more heat, and thus more energy.

Newton's Law of Cooling 3

Nevertheless, heat and temperature are related. As an object gains heat, its temperature will also increase. When talking about Newton’s Law of Cooling, it can actually be rearranged to create an equation to show the temperature as a function of time.

Law of cooling

Where Ts is the surrounding temperature, T0 is the initial temperature of the object, and k is a constant.

This equation looks pretty confusing, but all it essentially means is the temperature of an object will decay (or increase) to match the temperature of its surroundings. The change will happen quickly at first, but it will slow down as time goes on.

Newton's Law of Cooling

This theory allows scientists and engineers to correctly predict how certain materials will behave in different conditions. These types of calculations are done for anything from insulated coffee mugs to space rockets. They can then safely manufacture these to prevent any damage or harm.

Written By: Scott Yarbrough

Ready, Set, No Flinch Pendulum! Thats Science!

The conservation of energy tells us that a bowling ball won’t swing higher than the initial height if there is no force added. But should we still believe that in a high risk situation? We are putting the laws of physics up to the test.

Caution: Do not try this at home without parental supervision.

Sir Isaac Newton says the total energy an object has will alway stay the same, unless you do something to change it (push or pull it). The system will start with a certain amount of potential energy, the energy possessed by a body by virtue of its position relative to others. When you raise the bowling ball to face level you are putting energy into the system in the form of work. Work is done when a force is applied to an object and the object is moved through a distance.

pendulum

When you let go of the bowling ball and it starts to swing the ball will gain kinetic (or moving) energy, and lose it’s potential energy proportionally. This proportional loss and gain ensures the total energy of the system remains constant.

At the bottom of the pendulum (when the bowling ball is closest to the floor), all of the potential energy has been converted to kinetic energy. Therefore, the amount of kinetic energy in the ball is equal to the total energy of the system.

Pendulum science

On the upswing of the pendulum, the kinetic energy will start to convert back into potential energy. This will happen until it reaches your face, where there is no longer kinetic energy, but instead the potential energy is equal to the total energy.

This pattern of gain and loss of potential and kinetic energy would continue on and on in perfect conditions. However, here on Earth, there is no such thing as perfect. With each swing of the pendulum there is a little bit of energy lost due to friction in the rope. This loss of energy will dampen each swing, causing the maximum height of swing to go down each time.

science pendulum

This is a great way to test yourself to see if you trust in the laws of physics. Would you have to guts to face up to the no flinch pendulum?

 

Written by: Mimi Garai

Liquid Nitrogen Rocket! Here’s Why.

Every step you take is a tiny study in rocket science! Lift one foot and push backwards on the floor with the other. The floor exerts an equal and opposite (forward) force on the planted foot, and your body moves ahead.

Equal and opposite force pairs are everywhere. Stand on an ice rink and push against the wall; the wall pushes back, and you slide away. Sit in a chair, and your body pushes down against the seat, which pushes up with precisely the same force– if it didn’t, you’d fall! Birds push down on the air with their wings, and that air pushes their bodies upward.

NASA3rd

Image credit: NASA

The same process propels a rocket in motion. Thrusters shove fuel out behind a spacecraft. The fuel pushes back, equally and oppositely, and the rocket moves forward. Actual rocket fuel is accelerated backwards by explosive chemistry. We can model spaceflight in the lab with any expanding fuel whose flow can be directed.

Third law diagramLiquid nitrogen boils into gaseous form at -321 degrees Fahrenheit. This means if it is warmer than that, it will turn from a liquid to a gas that takes up 694 times as much space. We trapped this nitrogen in a ping pong ball with two very small holes on the sides. When the nitrogen expands, this is the only way out! The holes are positioned in opposite directions on opposite sides, and as the gas is directed out of these makeshift nozzles, the equal and opposite force due to Newton’s Third Law accelerates it to truly incredible speeds!

Actual rockets are meticulously designed for optimum aerodynamics and equipped with fins for stability. Ping pong balls are pretty much the opposite of that! Our tabletop rocket is all over the place. With some structural modifications, more stable motion might be possible. For now, though, we’re just having fun with this nitrogen-powered turbo top!

LNpingpong

Rockets & Newton’s Laws in 3 Gifs!

RocketLaunchRockets blast off from earth with a rumble and cloud of smoke on their way through the atmosphere to the vacuum of space beyond. This is something that is accepted today, but it hasn’t always been that way. Doctor Robert Goddard is known as the father of modern rocketry, but when he first postulated the current method of rocket propulsion in space, he was ridiculed. Even the New York Times published an article on the preposterousness of his ideas. Although rockets had been around for centuries, trying to use them in space was seen as ridiculous at the time.

The tools for understanding the basis of how a rocket works had been developed by Sir Isaac Newton hundreds of years earlier. Using Newton’s Laws of Motion, most of rocketry can be understood with relative ease.

His first law, often referred to as the law of inertia, states that an object in motion or at rest will remain in motion or at rest, respectively, unless acted upon by an outside force. This means that a rocket in space can turn its engines off and not slow down or even turn– unless an outside force, like gravity, acts on it. The bottle rockets in the video run out of fuel after a tiny fraction of a second, but they continue traveling upward until Earth’s gravity overcomes their momentum.

TennisBallsThis variation on the classic “pull out the tablecloth” trick is a great example of Newton’s first law. Nothing pushes or pulls the tennis balls sideways, so inertia mandates that they don’t move horizontally. For more cool inertia demonstrations, check out our blog post here.

Newton’s second law is most easily understood as an equation.

Screen Shot 2016-01-04 at 2.55.06 PM

FootOfScienceThe equation says that if you apply the same force to objects of two different masses, the lighter one will accelerate more than the heavier one. This shouldn’t be a surprise. If you kick a car with all your might, and then go kick a soccer ball with the same force, you will see (and feel) the difference! It’s easier to move or stop a light object than a heavy one.

The third and final law is what we like to call the law of interaction: for every action, there is an equal and opposite reaction. When a person stands, they push down on the ground, and the ground presses up equally on them. Imagine being on a frozen, icy lake, so slippery that you can’t walk. Normally, when you take a step, you push backwards against the ground, which in turn propels you forwards– an equal and opposite reaction. On an icy surface, you don’t have enough traction to push and move ahead this way. So, are you stuck? Not quite! Imagine standing on the ice and throwing a heavy rock. The rock exerts an equal and opposite force on you, pushing you in the other direction! Thinking this way makes a rocket easy to understand. Just like you can move across a slippery surface by throwing a heavy object away from you, a rocket can travel through the vacuum of space by shooting fire in the direction opposite its desired flight path.

WhiteboardBalloonA rocket doesn’t have to push against the air. It just throws fire out behind it, and the equal and opposite force thrusts it forward. As you can see, the basic idea behind rocket propulsion isn’t so complex after all.

So, what makes rocket science difficult in practice? Well, a rocket is basically a gigantic cylinder of explosive fuel with a nozzle to direct the explosion. The whole system moves at a very high speed. Without the right knowledge to control it, that’s a recipe for disaster! A rocket is also constantly launching its fiery fuel out behind it, so its mass is always changing. This makes calculations less than straightforward. As is the case in many fields, the core concepts in rocketry are simple. Complications arise when applying these ideas in real-world situations that require a lot of precision.

Shuttle

 

Blast-Off for the first space shuttle in 1981 from Kennedy Space Center. Credit NASA

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