Friction is the force that resists the sliding of surfaces along one another

Simulations suggest ice's slipperiness comes from rearranging molecules

Past models have proposed that slipperiness arises from a thin layer of liquid water formed at the ice's surface by frictional melting. However, new research suggests that electromagnetic forces between interacting surfaces push water molecules out of an ordered, crystalline structure and into a shapeless, soft, slippery layer. This process occurs solely through contact, independent of pressure or friction.

Viscosity is a fluid's resistance to flow, which varies with temperature

Liquids become less viscous as temperature increases, while gases become more viscous and therefore flow more slowly. The increased gas collisions at higher temperatures contribute to greater friction between streamlines, increasing viscosity.

Newton's laws describe how objects resist acceleration and respond to forces

Newton’s first law defines inertia as the tendency of an object to maintain its velocity. His second law connects external force, inertia, and acceleration, while his third law states that forces come in pairs—every action has an equal and opposite reaction.

Laminar flow moves in smooth, parallel layers, while turbulent flow is chaotic

In laminar flow, particles that make up a fluid move in consistent paths that do not cross each other. Contrastingly, differences across the speed of these particles cause them to mix, creating turbulence when viscosity cannot suppress the differences.

Electromagnetic repulsion prevents objects from making contact with one another

The feeling of touching something is a sensation caused by the electromagnetic force between the electrons on the surface of objects. Since this force grows to infinity with proximity, no two surfaces can ever achieve matter-to-matter contact.

Understanding why suction cups rely on Earth's atmosphere to work

When pressed against a surface, air is squeezed out of a sealed volume, causing the internal pressure to drop below the surrounding atmospheric pressure, and this imbalance creates the "sticking." For this reason, astronauts do not use suction cups or related technologies to stay on spacecraft during spacewalks.

O-rings contain fluid within a system

These donut-shaped components, typically made of rubber, block the escape of liquids and gases in low-pressure systems by forming a seal when compressed within a groove. In high-pressure systems, the O-ring is forced into a gap, blocking any leakage.

One of the leading theories behind muscle movement

According to the Sliding Filament Theory, skeletal muscle contraction is made possible by sarcomeres, which are made of bundles of myosin and actin proteins inside muscle cells. Myosin pulls itself along actin to contract a muscle, shortening the muscle and its cells and enabling physical movement. It then releases its grasp on actin so it can start the process over again if so commanded.

The most common types of touchscreens are capacitive and resistive

Capacitative screens are coated with a conductive material that creates a uniform electric field, which is disrupted by fingers. This disruption is registered by the device across a grid to determine where contact was made. Resistive screens identify touch when fingers push gap-separated sheets into contact with one another.

The marvels of mucus

Mucus—otherwise known as snot or phlegm—has a gross reputation, but the substance is actually of vital importance, lining the moist surfaces of our nose, intestines, lungs, and more. It plays a constant role in keeping our tissues from drying out and acts as a line of defense, but if it gets too sticky or thick, it can cause problems. Read about the marvels of mucus here.

Transpiration drives water movement through a plant’s vascular system

Water evaporates from the leaves, creating tension that pulls more water upward from the roots through the xylem—the equivalent of plant blood vessels. This process is supported by water molecules sticking to each other (cohesion) and xylem walls (adhesion).

The difference between cash flow and profit, explained

While cash flow is the net balance of cash moving in and out of a business, profit is the remaining balance after subtracting a business's operating expenses from its revenue.

What makes food crispy, and how science can be used to maximize this property

The fracturing texture experienced when biting into vegetable tempura, fried chicken, pastry crusts, and other foods comes from having a dehydrated, porous surface. When frying food in hot oil, trapped water vaporizes and escapes, creating tunnels and pores in the food as it dehydrates. Breading, particularly with the large, irregular shapes of panko, and leaveners can help create more air spaces.

Find fracking wells where you live and what chemicals operators are using

Fracturing fluid recipes are largely proprietary, but FracFocus has maintained a database of chemical disclosures since 2011. Today, the Department of Energy-affiliated nonprofit has more than 240,000 disclosures, along with a searchable database of fracking wells by state, county, and city.

Anatomy of a healthy knee joint

To understand arthritis, study a normal joint. Where two bones come together, each is lined by a cartilage cap. These bones are linked together by strong ligaments. The inner juncture is lined by a joint capsule (synovial membrane) containing lubricating joint fluid between the two surfaces, allowing for near-frictionless motion.

The San Andreas Fault is an example of tectonic plates sliding past each other

The transform boundary divides the opposing movements of the Pacific and North American tectonic plates, which create shear zones that distort and fracture rock. These movements produce shallow earthquakes as rocks are gradually displaced hundreds of miles.

Courts referee federalism disputes between Congress and the states

Modern federalism is primarily worked out through litigation. The Supreme Court decides disputes in written opinions that explain when federal law preempts state authority, how far Congress's powers extend, and when states may resist.

Falling demand and lower costs of production cause deflation

"Falling demand" refers to anything that changes someone's willingness to spend money on goods and services. Global recessions, fears of a worldwide recession, and a fall in the money supply are all factors that could lead to falling demand. Likewise, lower production costs allow companies to increase production, which can lead to a surplus in supply.

Hydroplaning occurs when a vehicle's tires lose traction on wet roads

Water depth must be over 0.1 inches, and vehicle speed must exceed 50 mph for hydroplaning to occur. Tire wear, size, and tread patterns affect the likelihood of hydroplaning, which is more common for all-wheel drive vehicles.

Fearology, or the study of fear, explores the difference between stress and fear

Our brains involuntarily respond to our environment and signal alarm when that isn’t always needed, triggering responses that include goose bumps. But understanding fear and how to talk our brains into calming down can improve daily life.

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

To reduce wrinkles in clothing, research recommends gentle wash cycles with more water and tumble drying with smaller loads and longer times.

The reflection of light within a material is the basis for fiber optics

As light travels from one material to another, it can be absorbed, reflected, or transmitted through, depending on the properties of the two materials. Fiber optic cables are designed to reflect light internally, minimizing data loss as information is sent at high speeds through flashes that represent zeros and ones.

HFMD can survive on surfaces for days at a time

That's why the virus can be transmitted via fomites—surfaces that have virus on them like doorknobs, kids toys, etc. These viruses are resilient—they are often even resistant to freezing (and are frequently stored at freezing temperatures in lab settings).

Grit: passion combined with perseverance over an extended time

Roughly defined as a balance of perseverance and passion, Angela Duckworth defines this combination as an essential component of reaching long-term goals. Not merely about talent or luck, Duckworth argues the personality trait enables individuals to maintain their commitment to significant objectives over extended periods, despite facing challenges and setbacks.

Catalysts increase chemical reaction rates by providing a lower energy pathway

All chemical reactions must overcome an energy barrier, called an activation energy, to proceed. If insufficient thermal energy exists in the system to overcome the barrier, catalysts can effectively lower the activation energy, increasing the likelihood of reactions occurring.

Dirty lightning is a thunderstorm created from friction between rising and falling flows of ash and smoke during volcanic eruptions.

How fusion—which releases energy when two lighter atoms combine to form a heavier atom—differs from fission

To reduce wrinkles in clothing, research recommends gentle wash cycles with more water and tumble drying with smaller loads and longer times.

The rivalry between Alexander Hamilton and Thomas Jefferson centered on federalism—the question of how much power the federal government should hold relative to the states.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

Doctors differentiate between a phobia and fear by asking patients whether their fear interferes with their day-to-day activities.

The boiling temperature of water decreases with increasing elevation because the molecules need less energy to overcome the lower atmospheric pressure associated with thinner air.

Some renewable energy sources may weaken the resiliency of electric grids by removing outage buffers provided by coal- and natural gas-fired plants, which provide the system with more time to find a new power source if a plant goes down.

The price of gas is a composite made up of several different factors, with the federal gas tax making up less than 20% of what drivers pay at the pump.

How Amazon operates a 'flywheel' business model, a self-reinforcing cycle that drives continuous growth

Hedge funds, the private investment firms that trade a wide swath of financial assets, make money by imposing steep fees on investors and from the fund's investment performance.

Ebola infects and disables immune cells, triggering a cascade of events that leads to small blood clots throughout the body, weakening blood vessels and interrupting blood flow to key organs.

Explore chaos in this simulation of two double pendulums, where small differences in the release angles produce wildly different outcomes.

An investigation suggests a Scottish island became awash in forever chemicals via seafoam and seaspray—raising questions about what that means for the safety of other coastal areas.

Corals are themselves not coral reefs—the term refers to the tiny marine invertebrates that build the rigid reef.

Objects can be 3D printed with light by projecting 2D computerized tomography (CT) scans onto rotating cylinders of resin, which solidify upon exposure.

Gerrymandering works through two techniques: cracking opposing voters across districts to dilute their power, and packing them into a few to waste their votes in lopsided majorities.

Some coin denominations have ridges etched on their sides, partly to prevent counterfeiting, in a practice called 'reeding.'

'Saturday Night Fever,' the 1977 film that introduced disco to the mainstream, was based on a fabricated magazine story.

The Brothers Grimm were lawyers before they were storytellers, but became interested in fairy tales as they began investigating how rules and customs had been passed down through cultures.

Poison ivy's characteristic rash is caused by an allergic response to an oily compound in the plant called urushiol.

The Russia-Ukraine conflict is the largest ground war in Europe since World War II in casualties, forces mobilized, and displacement of civilians.

The word 'jazz' evolved from 'jasm,' 19th-century American slang for 'energy'

Frank Lloyd Wright's houses are historically hard to sell because they're old, subject to local landmark commissions, and often unfashionable