Everyday Physics

Understanding the physics behind everyday phenomena and common questions

Subcategories

Electromagnetic Phenomena

Understanding everyday electromagnetic phenomena and electrical effects

Mechanical Phenomena

Understanding everyday mechanical phenomena and why objects behave as they do

Optical Phenomena

Understanding everyday optical phenomena and why we see what we see

Thermal Phenomena

Understanding everyday thermal phenomena and heat-related effects

Topics

Gears work by meshing teeth together to transfer rotation and torque between shafts. When one gear rotates, its teeth push against another gear's teeth, causing it to rotate. Gears can change speed, torque, and direction of rotation, providing mechanical advantage.

How do wheels work?

Wheels work by reducing friction through rolling motion. Instead of sliding (which has high friction), wheels roll, with the point of contact having zero velocity relative to the ground. This dramatically reduces friction, allowing heavy objects to be moved with much less force.

How does a lever work?

A lever works by using a rigid bar that pivots on a fulcrum. Applying force at one point creates a larger force at another point, allowing you to lift heavy objects with less effort. The mechanical advantage depends on the distances from the fulcrum to the force and load.

How does a pendulum work?

A pendulum works by converting between potential and kinetic energy as it swings. Gravity pulls the pendulum downward, and inertia carries it past the bottom, creating oscillating motion. The period (swing time) depends on length and gravity, not mass or amplitude.

What is centripetal force in everyday life?

Centripetal force is the force that keeps objects moving in circular paths, always pointing toward the center of the circle. In everyday life, centripetal force appears when cars turn (friction provides centripetal force), when objects swing in circles, and when planets orbit (gravity provides centripetal force).

Why do bicycles stay upright when moving?

Bicycles stay upright when moving due to a combination of factors: gyroscopic effects from spinning wheels, the caster effect (trail) from the front fork geometry, and active balancing by the rider. The spinning wheels create angular momentum that resists tilting, while the front fork geometry helps self-stabilize.

Why do objects fall at the same rate?

Objects fall at the same rate (in vacuum) because gravity accelerates all objects equally, regardless of mass. Heavier objects have more gravitational force, but they also have more mass, so the acceleration (force divided by mass) is the same for all objects.

Why do spinning tops stay balanced?

Spinning tops stay balanced due to angular momentum and gyroscopic stability. The spinning motion creates angular momentum that resists changes in orientation. When the top tilts, angular momentum causes it to precess (rotate around a vertical axis) rather than fall, maintaining balance.

Why do we feel weightless in space?

We feel weightless in space because we're in free fall—orbiting objects are constantly falling toward Earth, but their forward motion keeps them in orbit. Since everything falls together, there's no force pushing against us, creating the sensation of weightlessness.

Why do we have friction?

We have friction because surfaces are not perfectly smooth—microscopic bumps and irregularities interlock and resist motion. Friction helps us walk, grip objects, and control motion, making it essential for many everyday activities.

How do fiber optics work?

Fiber optics work by using total internal reflection to guide light through thin glass or plastic fibers. Light entering the fiber at angles greater than the critical angle reflects off the fiber walls, bouncing along the fiber without escaping. This allows light signals to travel long distances with minimal loss.

How do LED lights work?

LED (Light Emitting Diode) lights work by electroluminescence—when electric current flows through a semiconductor diode, electrons recombine with electron holes, releasing energy as photons (light). The semiconductor material determines the light color, and LEDs are highly efficient, converting most electrical energy into light.

How do mirrors create reflections?

Mirrors create reflections by having smooth, polished surfaces that bounce light back. When light hits a mirror, it reflects at the same angle it arrived (angle of incidence equals angle of reflection), creating clear, organized reflections that form images.

How do sunglasses work?

Sunglasses work by reducing the amount of light reaching your eyes through tinting (absorbing light) and often polarization (filtering specific light orientations). They protect eyes from bright light, reduce glare, and block harmful UV radiation.

Why do objects appear smaller in the distance?

Objects appear smaller in the distance due to perspective—the visual angle they subtend decreases with distance. As objects move farther away, they occupy a smaller angle in our field of view, making them appear smaller. This is a geometric effect of how light rays from distant objects reach our eyes.

Why do shadows form?

Shadows form because light travels in straight lines and cannot pass through opaque objects. When an object blocks light, it creates a dark region (shadow) where light cannot reach. The shadow's size and shape depend on the light source and object position.

Why do we see colors in soap bubbles?

We see colors in soap bubbles because of thin-film interference. Light reflects from both the front and back surfaces of the bubble film, and these reflections interfere. Different wavelengths interfere constructively or destructively at different film thicknesses, creating the colorful patterns we see.

Why do we see mirages?

We see mirages because hot air near the ground has different density than cooler air above, causing light to refract (bend). This creates the illusion of water or objects appearing where they don't exist, with the image often appearing inverted or distorted.

Why do we see stars twinkle?

Stars twinkle (scintillate) because of atmospheric turbulence. As starlight passes through Earth's atmosphere, it encounters varying air densities and temperatures that refract light. These rapid changes in refraction cause the star's apparent position and brightness to fluctuate, creating the twinkling effect.

Why do we see the moon during the day?

We see the moon during the day because the moon reflects sunlight, and when the moon is in the right position relative to the Sun and Earth, it's bright enough to be visible against the bright daytime sky. The moon is always in the sky about half the time, but we notice it more when it's visible during the day.

How does a refrigerator work?

A refrigerator works by using a refrigerant that evaporates inside (absorbing heat and cooling) and condenses outside (releasing heat). A compressor circulates the refrigerant, and the cycle continuously removes heat from inside the refrigerator, keeping it cold.

How does a thermometer work?

A thermometer works by using a substance that expands or contracts with temperature changes. Liquid thermometers use mercury or alcohol that expands in a narrow tube, with the height indicating temperature. Digital thermometers use temperature-sensitive electrical properties.

How does a thermos flask work?

A thermos flask (vacuum flask) works by minimizing heat transfer through three mechanisms: a vacuum between double walls prevents conduction and convection, reflective surfaces reduce radiation, and an insulated stopper prevents heat loss. This combination keeps hot liquids hot and cold liquids cold for extended periods.

How does an air conditioner work?

Air conditioners work by using a refrigeration cycle that transfers heat from inside to outside. A refrigerant circulates through coils, evaporating (absorbing heat) inside and condensing (releasing heat) outside. A compressor and expansion valve control the cycle, moving heat against the temperature gradient.

How does insulation work?

Insulation works by reducing heat transfer through conduction, convection, and radiation. Insulating materials trap air (a poor conductor), block convective currents, and reflect radiant heat. By creating barriers with low thermal conductivity, insulation slows heat flow, keeping warm spaces warm and cool spaces cool.

Why do we feel cold when wet?

We feel cold when wet because water evaporates from our skin, and evaporation requires energy (latent heat of vaporization). This energy comes from our body heat, cooling our skin and making us feel cold.

Why do we sweat when hot?

We sweat when hot because sweating cools the body through evaporation. When sweat evaporates from the skin, it absorbs heat energy (latent heat of vaporization), removing heat from the body. This cooling mechanism helps maintain body temperature within a narrow range despite external heat.

Why does hot air rise?

Hot air rises because it's less dense than cold air. When air is heated, molecules move faster and spread apart, decreasing density. Less dense air is buoyant and rises above denser cold air, creating convection currents that transfer heat upward.

Why does metal expand when heated?

Metal expands when heated because increased temperature makes atoms vibrate more, increasing the average distance between atoms. This thermal expansion occurs in all materials but is more noticeable in metals due to their rigid structure and common use in construction.

Why does wind feel cold?

Wind feels cold because it increases heat loss from your body through convection and evaporation. Moving air removes the warm air layer around your skin and increases evaporation of moisture, both of which cool your body faster than still air.