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Heat is a form of energy that moves from hot to cold. Heat can increase the kinetic energy of matter, or thermal energy inside matter. The atoms in hotter masses bounce! The atoms in colder masses do not bounce as much.
Temperature is a measure of the average kinetic energy in matter; hot molecules are bouncier than cold molecules. Temperature measures the bounciness of atoms that make up matter.
Heat is the flow of thermal energy and it can move in three different ways:
Conduction
Conduction
Conduction is the transfer of energy through matter from particle to particle. It is the transfer and distribution of heat energy from atom to atom within a substance.
For example, a spoon 🥄 in a cup ☕️ of hot chocolate becomes warmer because the heat from the soup is conducted along the spoon.
Conduction is most effective in solids-but it can happen in fluids.
Fun fact: Have you ever noticed that metals tend to feel cold? Believe it or not, they are not colder! They only feel colder because they conduct heat away from your hand. Metals are great conductors of heat. You perceive the heat that is leaving your hand as "cold." 🥶
Convection
Convection
Convection is the transfer of heat by the actual movement of the warmed matter.
☕️Heat leaves the coffee cup as the currents of steam and air rise. Convection is the transfer of heat energy in a gas or liquid by the movement of currents. (It can also happen in some solids, like sand.)
The heat moves with the fluid.
Consider this: convection is responsible for making macaroni rise and fall in a pot of heated water. The warmer portions of the water are less dense and therefore, they rise. Meanwhile, the cooler portions of the water fall because they are denser.
Radiation
Radiation
Radiation: Electromagnetic waves that directly transport ENERGY through space. This type of heat transfer does not require matter. But it can still travel through matter.
🌞Sunlight is a form of radiation that is radiated through space to our planet 🌎 without the aid of fluids or solids.
The energy travels through nothingness! Just think of it! The sun transfers heat through 93 million miles of space. Because there are no solids (like a huge spoon) 🥄 touching the sun🌞 and our planet,🌎 conduction is not responsible for bringing heat to Earth. 🌎
Since there are no fluids (like air and water) in space, convection is not responsible for transferring the heat.
Thus, radiation brings heat to our planet.
Radiometer
Radiometer
How a radiometer works: There is a partial vacuum in the radiometer. It needs some air molecules to work. With too much air, it will not spin.
Heat excites the black surface of the vanes more than it heats the white surface. Black is a good absorber and a good radiator. Think of black as a large doorway that allows heat to pass through easily. In contrast, white is a poor absorber and a poor radiator of energy. White is like a small doorway and will not allow heat to pass easily.
The black molecules bounce and push against the limited air molecules. According to Newton's 3rd Law, if the air is pushed one way, then the vane moves the other direction.
The difference in temperature between the warm, black side and the cooler white side causes gasses to creep along the surface of the vanes. This effect is known as "thermal creep." The faster gasses from the black side strike the edges of the vane at an angle with more force than the molecules from the cold side. The equal and opposite forces cause the radiometer to spin. More information about this.
Why a radiometer runs backward after the light is turned off. Heat escapes quickly from the black sides of the vanes. Thus, the black molecules cool off first. Meanwhile, the white molecules take longer to lose heat cool down. The result is that gasses from the white vane push off with more force (Newton's third law) and the vanes spin in the opposite direction.
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