Imagine a basketball. An everyday, ordinary basketball sitting perfectly still on an empty court. Now visualize a player — let’s go with Diana Taurasi of the WNBA’s Phoenix Mercury. She saunters out to midcourt, her shoes squeaking against the hardwood planks. Then Taurasi bends down, grabs the ball, stands back up and raises it over her head.
You have just witnessed an increase in the ball’s potential energy.
For the record, this is just one of the many types of energy we encounter on a daily basis. There’s also kinetic energy, electrical energy, thermal energy and so on.
This begs a fundamental question. Scientifically, what is energy? What does that word mean in the context of physics, chemistry, engineering and related STEM fields?
Here’s the definition you’re most likely to hear in your Advanced Placement courses or find in a textbook:
“Energy is the ability to do work.”
Taken by itself that sentence might seem kind of vague and not especially helpful. But don’t worry, we’re here to help you unpack it.
Now, when the textbooks say energy is “the ability to do work,” they’re not just talking about 9 to 5 employment. In a nutshell, the scientific meaning of the word “work” is the process of moving an object by applying force to it.
“Whenever a force is applied to an object, causing the object to move, work is done by the force,” according to Boston University.
As for energy, it comes in two basic categories: kinetic energy and potential energy.
K.E. Goes to Hollywood
Sometimes, kinetic energy is described as “the energy of movement.” To possess this kind of energy, an object must be in motion.
Remember the Texas-sized asteroid that came streaking toward Earth in Michael Bay’s 1998 blockbuster “Armageddon”? In real life that thing would’ve had some serious kinetic energy. So do speeding cars, falling apples and other moving objects.
Grab a pencil, folks, because we’re about to throw an equation at you:
K.E. = (1/2)m x v2
Translation: An object’s kinetic energy (“K.E.”) equals one-half of its mass (“m”) times its velocity squared (“v2“).
Time to break that down with an example. What is the kinetic energy of a 400-kilogram (or 882-pound) horse galloping at a velocity of 7 meters per second (23 feet per second)?
Expressed numerically, here’s what the problem looks like:
K.E. = (1/2) 400 x 72
Plug in the numbers and you’ll find that the kinetic energy possessed by our noble steed is equal to 9800 joules. For the record, joules (abbreviated as “J”) are a unit of measurement scientists use to quantify energy or work.
So Much Potential
If kinetic energy is “the energy of movement,” then potential energy is “the energy of position.”
Let’s check back in with Diana Taurasi. What do you think is going to happen the instant she lets go of that ball, the one we said she’d lifted high up off the ground?
Of course, it’ll fall and hit the hardwood floor. All because of a little thing called gravity. (To keep things simple here, we’re assuming the WNBA star didn’t actively push or throw the ball.) And as we now know, the moving object will exhibit kinetic energy on the way down.
But before the drop, before the ball leaves Taurasi’s hands, it’s going to contain a fair bit of potential energy.
Potential energy is stored energy. It’s the energy that an object (Taurasi’s ball in this case) has thanks to its position relative to other objects, like the solid floor. Why do we call this phenomenon “potential energy”? Because it introduces the potential for a force — such as gravity — to do work.
Neither Created Nor Destroyed
Note that there are different kinds of potential energy. The one we discussed in our basketball example is called gravitational potential energy or just “gravitational energy.”
To quote the U.S. Energy Information Administration website, this is a type of potential energy “stored in an object’s height. The higher and heavier the object, the more gravitational energy is stored.”
By raising her ball off the ground, Taurasi gave gravity the potential to do work with it. If she’d made like a Harlem Globetrotter and carried the ball to the top of a high circus ladder — or if she’d lifted a heavy bowling ball instead of a lightweight basketball — there’d be even more gravitational potential energy at play.
Mind you, this energy won’t just go away when Taurasi releases the ball. Within the confines of a closed system (such as our universe), energy can neither be created nor destroyed. It simply transforms.
As it plunges toward the hardwood, that ball’s gravitational potential energy is going to decrease because it’s getting closer to the floor. And upon touching the ground, the ball (functionally) won’t have any gravitational potential energy at all.
Yet as the ball zooms downward and loses gravitational potential energy along the way, there will be a simultaneous increase in its kinetic energy.
Flavors of Energy
Our story doesn’t end once the ball hits those floor panels. Some of its energy will be converted into thermal energy and thus generate some heat.
Oh, and that lovely “thunking” noise basketballs make when they bounce? That’s a kind of energy too, one that most people call sound.
Other kinds of energy include electrical energy, mechanical energy and radiant energy.
Before parting ways, we’ll leave you with some last-minute definitions.
- Thermal Energy: This is the internal movement and vibration of the atoms and molecules within an object or substance. When thermal energy flows between objects or substances, we call that transfer “heat.”
- Sound: This is energy that’s caused by vibration and travels through substances in longitudinal waves.
- Electrical Energy: A type of kinetic energy, this is the movement of electrical charges which may result when force is applied to atoms.
- Radiant Energy: This is the kind of energy you get from electromagnetic radiation. Light falls into this category.
- Chemical Energy: File this one under “potential energy.” It’s the energy stored in bonds that hold atoms together.
- Gravitational Energy: Also called “gravitational potential energy,” this would be the potential energy an object derives from its placement within a space that experiences gravity.
Global Warming Causes Fewer Tropical Cyclones
But having fewer hurricanes and typhoons does not make them less of a threat. Those that do manage to form are more likely to reach higher intensities as the world continues to heat up with the burning of fossil fuels.
Scientists have been trying for decades to answer the question of how climate change will affect tropical cyclones, given the large-scale death and destruction these storms can cause. Climate models have suggested the number of storms should decline as global temperatures rise, but that had not been confirmed in the historical record. Detailed tropical cyclone data from satellites only go back until about the 1970s, which is not long enough to pick out trends driven by global warming.
The new study worked around those limitations by using what is called a reanalysis: the highest-quality available observations are fed into a weather computer model. “That’s something which gets us close to what the observation would have looked like,” essentially “filling in the gaps,” says study co-author Savin Chand, an atmospheric scientist at Federation University Australia. This gives researchers a reasonably realistic picture of the atmosphere over time, in this case going back to 1850. Chand and his team developed an algorithm that could pick out tropical cyclones in that reanalysis data set, enabling them to look for trends over a 162-year period.
They found the 13 percent global decrease in tropical cyclones over the period of 1900 to 2012, compared with 1850 to 1900 (the latter is widely considered a pre-global-warming reference period). There was an even larger decline of about 23 percent since around 1950, around the time global temperatures started to noticeably rise. The declines vary in different parts of the ocean. For example, the western North Pacific saw 9 percent fewer storms, and the eastern North Pacific saw 18 percent fewer over the 20th and early 21st centuries. And the North Atlantic results indicated a peculiar trend, showing an overall decrease over the past century—but with an uptick in recent decades. That shorter-term increase could be linked to natural climate variations, better detection of storms or a decrease in aerosol pollution (because aerosols have a cooling effect, and tropical cyclones thrive on warm waters).
The study provides crucial ground-truth information for evaluating climate model projections of further future changes in cyclone frequency, says Kimberly Wood, a tropical meteorologist at Mississippi State University, who was not involved with the paper.
Chand and his colleagues link the decrease in tropical storm frequency to changes in atmospheric conditions that constrict convection—the process where warm, moist air surges upward in the atmosphere, which allows tropical cyclones to develop from small weather disturbances that act as the “seeds.” The researchers think those changes are caused by warming-driven shifts in global atmospheric circulation patterns. “It’s a pretty holistic view,” Wood says of the analysis.
But even if there are fewer tropical cyclones overall, a larger proportion of those that do form are expected to reach higher intensities because global warming is also raising sea-surface temperatures and making the atmosphere warmer and moister—the conditions these storms thrive on. “Once a tropical cyclone forms,” Chand says, “there is a lot of fuel in the atmosphere.”
ABOUT THE AUTHOR(S)
Andrea Thompson, an associate editor at Scientific American, covers sustainability. Follow her on Twitter @AndreaTWeather Credit: Nick Higgins
The effect of breast cancer screening is declining
Screening for breast cancer has a cost. This is shown by a Danish/Norwegian study that analysed 10,580 breast cancer deaths among Norwegian women aged 50 to 75 years.
“The beneficial effect of screening is currently declining because the treatment of cancer is improving. Over the last 25 years, the mortality rate for breast cancer has been virtually halved,” says Henrik Støvring, who is behind the study.
According to the researcher, the problem is that screenings lead to both overdiagnosis and overtreatment, which has a cost both on a human level and in terms of the economy.
Overdiagnosis and overtreatment
When the screening was introduced, the assessment was that around twenty per cent of the deaths from breast cancer among those screened could be averted. While this corresponded to approximately 220 deaths a year in Denmark 25 years ago, today the number has been halved.
The study shows that in 1996 it was necessary to invite 731 women to avoid a single breast cancer death in Norway, you would have to invite at least 1364 and probably closer to 3500 to achieve the same result in 2016.
On the other hand, the adverse effects of screening are unchanged.
“One in five women aged 50-70, who is told they have breast cancer, has received a ‘superfluous’ diagnosis because of screening — without screening, they would never have noticed or felt that they had breast cancer during their lifetime,” says the researcher.
One in five corresponds to 900 women annually in Denmark. In addition, every year more than 5000 women are told that the screening has given rise to suspicion of breast cancer — a suspicion that later turns out to be incorrect.
Peaceful, small nodes — but in who?
Henrik Støvring notes that the result is not beneficial for the screening programmes. According to him, the Norwegian results can also be transferred to Denmark. Here, women between 50 and 69 are offered a mammogram screening every second year. This is an X-ray examination of the breast, which can show whether the woman has cellular changes that could be breast cancer.
The Danish screening programme became a national programme offered to all woman in the age group in 2007 — three years after the Norwegians. Approx. 300,000 Danish women are invited to screening for breast cancer every year.
According to the researcher, the challenge is that we are not currently able to tell the difference between the small cancer tumours that will kill you and those that will not. Some of these small nodes are so peaceful or slow-growing that the woman would die a natural death with undetected breast cancer, if she had not been screened. But once a cancer node has been discovered, it must of course be treated, even though this was not necessary for some of the women — we just do not know who.
“The women who are invited to screening live longer because all breast cancer patients live longer, and because we have got better drugs, more effective chemotherapy, and because we now have cancer care pathways, which mean the healthcare system reacts faster than it did a decade ago,” says Henrik Støvring.
Materials provided by Aarhus University. Original written by Helle Horskjær Hansen. Note: Content may be edited for style and length.
Thin-film photovoltaic technology combines efficiency and versatility
Stacking solar cells increases their efficiency. Working with partners in the EU-funded PERCISTAND project, researchers at the Karlsruhe Institute of Technology (KIT) have produced perovskite/CIS tandem solar cells with an efficiency of nearly 25percent- the highest value achieved thus far with this technology. Moreover, this combination of materials is light and versatile, making it possible to envision the use of these tandem solar cells in vehicles, portable equipment, and devices that can be folded or rolled up. The researchers present their results in the journal ACS Energy Letters.
Perovskite solar cells have made astounding progress over the past decade. Their efficiency is now comparable to that of the long-established silicon solar cells. Perovskites are innovative materials with a special crystal structure. Researchers worldwide are working to get perovskite photovoltaic technology ready for practical applications. The more electricity they generate per unit of surface area, the more attractive solar cells are for consumers
The efficiency of solar cells can be increased by stacking two or more cells. If each of the stacked solar cells is especially efficient at absorbing light from a different part of the solar spectrum, inherent losses can be reduced and efficiency boosted. The efficiency is a measure of how much of the incident light is converted into electricity. Thanks to their versatility, perovskite solar cells make outstanding components for such tandems. Tandem solar cells using perovskites and silicon have reached a record efficiency level of over 29percent, considerably higher than that of individual cells made of perovskite (25.7percent) or silicon (26.7percent).
Combining Perovskites with CIS for Mobility and Flexibility
Combining perovskites with other materials such as copper-indium-diselenide (CIS) or copper-indium-gallium-diselenide (CIGS) promises further benefits. Such combinations will make it possible to produce light and flexible tandem solar cells that can be installed not only on buildings but also on vehicles and portable equipment. Such solar cells could even be folded or rolled up for storage and extended when needed, for example on blinds or awnings to provide shade and generate electricity at the same time.
An international team of researchers headed by Dr. Marco A. Ruiz-Preciado and tenure-track professor Ulrich W. Paetzold from the Light Technology Institute (LTI) and the Institute of Microstructure Technology (IMT) at KIT has succeeded in producing perovskite/CIS tandem solar cells with a maximum efficiency of 24.9percent (23.5percent certified). “This is the highest reported efficiency for this technology and the first high efficiency level reached at all with a nearly gallium-free copper-indium diselenide solar cell in a tandem,” says Ruiz-Preciado. Reducing the amount of gallium results in a narrow band gap of approximately one electron volt (eV), which is very close to the ideal value of 0.96eV for the lower solar cell in a tandem.
CIS Solar Cells with Narrow Band Gap- Perovskite Solar Cells with Low Bromine Content
The band gap is a material characteristic that determines the part of the solar spectrum that a solar cell can absorb to generate electricity. In a monolithic tandem solar cell, the band gaps must be such that the two cells can produce similar currents to achieve maximum efficiency. If the lower cell’s band gap changes, the upper cell’s band gap has to be adjusted to the change, and vice versa.
To adjust the band gap for efficient tandem integration, perovskites with high bromine content are usually used. However, this often leads to voltage drops and phase instability. Since the KIT researchers and their partners use CIS solar cells with a narrow band gap at the base of their tandems, they can produce their upper cells using perovskites with low bromine content, which results in cells that are more stable and efficient.
“Our study demonstrates the potential of perovskite/CIS tandem solar cells and establishes the foundation for future development to make further improvements in their efficiency,” says Paetzold. “We’ve reached this milestone thanks to the outstanding cooperation in the EU’s PERCISTAND project and, in particular, thanks to our close cooperation with the Netherlands Organisation for Applied Scientific Research.” Important groundwork was done in the CAPITANO project funded by Germany’s Federal Ministry for Economic Affairs and Climate Action (BMWK).
Materials provided by Karlsruher Institut für Technologie (KIT). Note: Content may be edited for style and length.
Entertainment3 weeks ago
At Long Last, the First Portrait of Lilibet Mountbatten-Windsor Is Here
Science3 weeks ago
Wow! International Space Station and Boeing Starliner captured in the same incredible image
Top News3 weeks ago
Shari Puorto Band performs at Beaver Creek, CO’s Blues, Brews & BBQ Festival, 2022
Top News2 weeks ago
Italy minister says nationalisation an option for Lukoil refinery
Technology3 weeks ago
Save over $650 off an unlimited lifetime subscription to Offcloud
Entertainment3 weeks ago
25 Of The Best Candid Royal Family Moments From The Platinum Jubilee
Science3 weeks ago
How to Change the Alarm Volume on iPhone
Sports3 weeks ago
Michael Bisping shares his take on the biggest UFC fight that failed to come to fruition: “That truly is the one that got away”