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.

Is ice slippery because of amorphization—a chaos of molecules caused by sliding?

Traditional explanations cite three factors that make ice slippery: pressure, friction and so-called premelting. A fourth has been proposed in recent years: amorphization, that sliding along some surfaces creates molecular disorder, causing liquid-like behavior.

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.

The centrifugal force is associated with the feeling of being pushed outward when moving in a circle, but it is a fictitious force arising from objects' tendency to move in straight lines.

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.

The Navier-Stokes equations include the fluid version of Newton's second law

The first equation is the fluid version of the conservation of mass, which prevents incompressible fluids from gaining or losing matter. The second equation replaces acceleration and inertia, which is resistance to acceleration, with fluid pressure and viscosity.

The Reynolds number is the ratio of viscous and inertial forces in fluids

It can approximate fluid behavior in simple systems by non-dimensionalizing—removing the units within—the Navier-Stokes equations. A value close to zero indicates that the fluid will exhibit laminar flow, while a large number suggests that turbulence will occur.

Turbulence has been called the most important unsolved problem in classical physics

Despite being the most common type of fluid flow in our world, scientists have struggled to model turbulent flow accurately. Though behaving unpredictably, understanding inertia and viscosity can help determine whether turbulence will occur.

You have never made physical contact with anything in your life because electrons in the outer layer of atoms on the surface of objects repel one another.

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.

Simulate the buildup and discharge of static electricity through friction by dragging the arm and leg of 'John Travoltage' along surfaces.

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.

When experiencing turbulence, fluid elements undergo stretching and folding

Simulations show patches of fluid particles, such as splashes of milk, bend under turbulent flow, creating curvature that grows linearly then exponentially. This accelerated deformation enhances folding and mixing faster than other methods, such as stirring or beating.

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.

While landslides are associated with the downward flow of unstable terrain, the term encompasses a variety of geological processes, which are distinguished by how the material moves and what materials are involved.

Explaining the Leidenfrost effect, where water can hover and move against gravity

Water droplets can glide across surfaces whose temperatures are well above water's boiling point. This heat instantly vaporizes the bottom of the droplet, creating a layer of steam that the rest of the droplet rides and bounces upon. This can be seen when sprinkling water on skillets to determine if the surface is hot enough to cook on.

Winter Olympic sports highlight various laws and principles of physics

Figure skaters leverage the conservation of angular momentum during spins by tightening their bodies, and the skintight suits used in ski jumping help reduce drag. Centripetal force allows speedskaters to make tight turns, while friction on skis helps ski mountaineers climb slopes. No action can violate the conservation of energy.

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.

Some tectonic plates move faster than their underlying convection currents

Like a chain slipping off a ledge, as tectonic plates sink, their weight can pull the rest of the trailing plate forward, accelerating their movement. Plates can also break apart and fall, creating a suction effect that drives movement, resembling leaves following a passing car.

Once cooled to temperatures just above 2 Kelvin, helium atoms exhibit a quantum property that removes internal friction, allowing the fluid to climb up walls.

Fracking provides access to fossil fuel reserves locked in underground rock

Using a pressurized fluid mixture that is over 90% water, cracks are created in shale about 2 miles deep to release trapped oil and natural gas. The process uses an average of 3 to 6 million gallons of water per well, which can strain local water supplies.

Differences in pressure and temperature between atmospheric gases create wind

Because Earth's surface is not uniformly heated by the sun at all times, pockets of warmer and cooler air will form and interact. Warmer pockets of less dense air will rise, leaving gaps for cooler, denser air to move in. Wind is this movement of air from high-pressure to low-pressure areas.

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.

Iron rusts in the presence of water and oxygen because these ingredients enable the metal atoms to release energy and enter a more stable state.

Slab pull and ridge push contribute to convection-driven oceanic crust movement

Through ridge push, after magma is projected up from the mantle, it cools and sinks, allowing gravity to help push older oceanic crust away. As this crust sinks into the mantle at deep-sea trenches, it pulls on the trailing crust behind it, accelerating ocean crust movement.

Gravity, electromagnetism, and two nuclear forces make up nature’s fundamental forces

While gravity is the most familiar force, it is also the weakest and the only one without a particle to mediate the force. The weak nuclear force is responsible for radioactive decay and transmutation of elements, while the strong nuclear force holds quarks together.

Oil and natural gas from fracking is considered unconventional

This method forcibly extracts fossil fuels from tightly packed rocks, where they form from organic matter that has undergone extreme heat and pressure. Conventional drilling, on the other hand, waits for the oil and gas to escape from shale and accumulate in more porous and permeable rocks, such as limestone.

Convection flows in Earth’s mantle drive the movement of tectonic plates

These processes transfer heat from Earth’s core to the surface via rising magma plumes, while cooler, denser rock falls into the mantle at rates similar to human fingernail growth. These rates are determined by combining seismic data with computer simulations to model Earth’s interior.

Adhesion molecules and intercellular junctions allow cells to connect together

While some organic structures are mostly composed of non-cellular components (e.g., collagen and calcium phosphate minerals in bones), tissues and organs composed of connected cells rely on specialized proteins and connections to create watertight seals that protect cells within the interior from environmental molecules.

Understanding turbulence, which is characterized by growing chaos at multiple scales

As energy is lost in fluids undergoing turbulent, non-linear flow, particles will collectively form eddies, or whirlpools, of various sizes that mix together. The energy cascade of larger eddies becoming smaller ones before dissipating completely varies based on the initial conditions of the fluid, a characteristic feature of chaotic systems.

High freezing speed restricts the development of gritty crystal chunks in ice cream

For this reason, ice cream does not maintain its smoothness when refrozen in a traditional freezer over several hours. The smooth texture is also made possible by balancing fat, sugar, and emulsifiers.

Classical mechanics describes the motion of and forces on everyday objects

Newton's laws form the core of classical mechanics, suitable for everyday objects and speeds. The term is relatively new, distinguishing the branch of physics from quantum and relativistic mechanics.

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 solar system's planets orbit in the same direction in a nearly flat disc because the particles that made up the gas cloud from which the system formed had an initial, overall plane of rotation.

Gravity assists are crucial for space travel beyond Mars

By traveling near a moving celestial object, a passing object can gain or lose speed and change direction due to the acceleration provided by their mutual gravity. Some missions are planned around spacecraft performing multiple assists, or slingshots, to reduce fuel requirements for long-distance travel.

Beyond a certain pressure and temperature, matter can become a supercritical fluid—an exotic state of matter that simultaneously exhibits properties of gases and liquids.

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.

The turbulence experienced in airplanes results from unexpected changes in airflow

Pilots rely on forecasts, onboard tools, and air traffic control to avoid regions of severe turbulence during flight. Turbulence is generally weaker for those sitting in the front of the main cabin and for morning flights that follow cooler nighttime temperatures.

Teflon was an accidental discovery by a DuPont scientist in the 1930s resulting from efforts to create a safe refrigerant.

Mathematics proves turbulence's chaos creates super diffusion

Turbulent flow is responsible for the rapid scattering of dandelion seeds, volcanic ash, and untied balloons. Its swirling behavior accelerates particle scattering faster than other mixing methods, as particles acquire energy from the interactions of eddies.

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.

Lightning is the sudden flow of electricity in the atmosphere as two oppositely charged regions seek to become balanced via the movement of electrons.

How do touchscreens work?

Touchscreens have revolutionized digital interactions, but how they work widely varies depending on the device. Explore the history and workings of the most common types—capacitive and resistive—and new interaction methods incorporated into foldable screens and touchless interfaces.

A human joint is any place in the human body where two bones connect, providing structure and stability.

Wind is the movement of air caused by the sun's uneven heating of Earth

The tilt, curvature, and variations in Earth's surface composition across the globe cause different regions to receive different amounts of solar radiation. As the Earth spins and tries to achieve thermal equilibrium, air masses move and interact, creating wind.

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.

Debating whether water is or is not wet depends on one's definition of wetness

If defined as a liquid sticking to a surface, then water itself is not wet. The sensation of "wetness" arises from water molecules latching onto an object. This occurs because water is a polar molecule possessing local regions of positive and negative charge that are attracted to charge imbalances on the surface of materials.

Blood clotting is critical to maintaining life, but dysfunctional clots can be fatal.

See the anatomy of a healthy knee joint, which has smooth cartilage that cushions the joints and protects the bones from rubbing together.