Unit 2: Activity 1: What factors affect material changes
Substances may change due to external factors such as air, water, and temperature, some change quickly, some slower, and remain stable after long-term action.
The speed of change in matter is faster The phenomenon of change in matter is slower
For example, ice cubes turn into water, cut apples change color, chocolate becomes soft, wood burns, fresh milk spoils at room temperature, etc. For example, rocks change shape, blades or nails rust, old books or paper turn yellow, bicycles rust, etc.
Exposure to the sun, rubbing hands, using electric heaters, and starting fires can generate heat and raise the temperature.
In addition to physical sensations, using a thermometer can accurately determine temperature changes.
Activity 2: What changes does temperature change affect water? 1. When the ice is heated, the shape will change. The phenomenon of solid ice turning into liquid water is called melting. 2. The phenomenon of ice melting into water such as ice floes at sea melting and becoming smaller, ice cubes in drinks melting and becoming smaller after a period of time, popsicles melting and softening after taking out of the refrigerator for a while, snow melting in spring, etc. 3. The rate of ice melting will be affected by temperature, the higher the temperature, the faster the ice melts. 4 Water turns into invisible water vapor under natural circumstances and is dispersed in the air. The phenomenon of liquid water turning into gaseous water vapor is called evaporation. 5. Using sun exposure, increasing temperature, wind blowing, and increasing the air contact area can speed up the evaporation of water. 6. The phenomenon of water evaporating into water vapor, such as drying daylilies in the sun, blowing hair with a hair dryer, opening a wet umbrella to dry, etc. 7When the temperature of water drops below 0°C, it turns into ice. The phenomenon of liquid water turning into solid ice is called solidification. 8 Water vapor will turn into small water droplets when cold, and the phenomenon of gaseous water vapor turning into liquid water is called condensation. 9. The phenomenon of water vapor condensing into small water droplets such as white smoke when it is cold, foggy glasses lenses when eating hot food, and many small water droplets condensing on the lid of a pot containing hot soup. 10The white smoke that you see when boiling water is small water droplets formed by water vapor condensation.
Activity 3: What is the effect of temperature changes on other substances?
1. Water, ice, and water vapor are the three different forms of water, and when the temperature changes, the shape of water changes:
【Ice (solid state) heats up and melts into water (liquid state), and water cools down and freezes into ice; water (liquid state) heats up and evaporates into water vapor (gaseous state), and water vapor cools down and condenses into water.】
2. Ice is solid and has a fixed shape, and will not change shape with the container; Water is liquid and has no fixed shape and changes shape with the container.
3. Changes in other substances:
(1) Some substances change their shape after being heated, and then return to their original form after cooling, such as chocolate, wax, etc.
(2) After being heated, some substances change their form and properties, and cannot return to their original form, such as corn kernels, charcoal, etc.
