Heat Energy

Temperature measures how hot or cold something is based on the movement of its particles. When particles move faster, temperature is higher; when they move slower, it's lower. Think of it like this: when you heat water on your mother's stove, the water molecules move faster and faster until the water boils.

We measure temperature using thermometers with two main scales. The Celsius scale (°C) marks water's freezing point at 0°C and boiling point at 100°C—perfect for our climate. The Kelvin scale (K) is used in science and starts at absolute zero, the coldest possible temperature.

A practical Nigerian example: when checking if a baby has fever, the thermometer reading shows temperature. Normal body temperature is about 37°C. Temperature differs from heat; heat is the energy that flows from hot to cold objects.

When heat energy is applied to any substance, it causes changes in the matter. The most common effect is thermal expansion, where materials increase in size as temperature rises. This happens because heat makes particles move faster and take up more space. Contraction occurs when heat is removed and particles slow down.

Think about the metal roofing sheets on Nigerian houses during the hot harmattan season. They expand during the day's intense heat, which is why they sometimes make creaking sounds. At night when temperatures drop, they contract back. This is also why gaps are left between railway tracks in Nigeria—to prevent buckling during expansion.

Heat can also cause changes in state, like water boiling into steam or ice melting into liquid water. Some materials may even become softer when heated, like the rubber soles of shoes left in direct sunlight.

When heat energy enters a substance, the particles inside start moving faster. This faster movement is what we call rise in temperature. Think of it like this: when you put a pot of water on a hot stove, the heat from the fire makes water molecules vibrate and move more rapidly, and the thermometer reading goes up. That's a rise in temperature.

The amount of temperature increase depends on how much heat energy you add and what material you're heating. Some materials like metals heat up quickly, while others like water need more heat energy to show the same temperature rise. During the JAMB and WAEC exams, you'll see questions about this relationship between heat energy and temperature change.

A practical Nigerian example is heating palm oil in a cooking pot. When you turn up the flame, the palm oil's temperature rises noticeably within minutes because oil has low heat capacity compared to water.

When heat energy is applied to a substance, its particles gain energy and move faster. This increased movement can cause the substance to change from one state to another—solid to liquid, liquid to gas, or even solid directly to gas. We call this change of phase state.

Think about making ice cream on a hot Lagos afternoon. Your solid ice cream melts into liquid as heat energy enters it. If you leave it long enough in the sun, some of that liquid will evaporate into water vapour. These are phase changes happening right before your eyes. Each change requires a specific amount of heat energy called latent heat.

The reverse also happens: cooling removes energy and allows gases to condense into liquids, and liquids to freeze into solids. Understanding these changes helps explain everyday phenomena from boiling water to clothes drying on a line.

When materials get hot, their particles move faster and push further apart, causing the material to expand or grow bigger. This happens in solids, liquids, and gases. Think about railway tracks in Nigeria—during the hot harmattan season, the metal expands and can buckle if there's no space left for growth. That's why railway engineers deliberately leave gaps between rail sections.

Different materials expand at different rates. This property is measured using the coefficient of linear expansion. Water behaves unusually; it actually contracts when heated from 0°C to 4°C, then expands normally after that. This unusual behavior is crucial for aquatic life survival during winter.

Understanding expansion helps engineers design buildings, bridges, and pipelines that won't crack or fail during temperature changes. It's a fundamental concept that appears constantly in thermal physics questions.

The resistance of a conductor changes when temperature changes. When you heat a metal wire, the atoms vibrate more vigorously, causing more collisions between moving electrons and atoms. These extra collisions make it harder for current to flow, so resistance increases. Most metals behave this way—their resistance grows as temperature rises.

Think of a light bulb filament in your home. When electricity passes through it, the filament heats up and glows. As the temperature increases, the resistance of the filament wire also increases. This is why the brightness sometimes changes slightly when you first switch on a bulb—the resistance is still increasing as the filament warms up.

The relationship between resistance and temperature is expressed mathematically: R = R₀(1 + αt), where α is the temperature coefficient of resistance. Different materials have different α values.

When objects get hot, they expand because heat makes their particles move faster and take up more space. We measure this expansion in three ways. Linear expansivity tells us how much length increases when temperature rises by one degree. Area expansivity measures how surface area expands, and volume expansivity shows how the whole 3D space increases. Think about railway tracks in Nigeria – during hot harmattan weather, the metal expands, so engineers leave gaps between sections to prevent buckling and accidents. If we didn't account for this expansion, trains would derail. The coefficients for these expansivities are different for different materials, which is why some materials are better suited for certain jobs. Water behaves unusually because it contracts as it cools from 4°C to 0°C, which is why ice floats.