Unit 4P.2: Heat and Temperature

Transcription

1 Unit 4P.2: Heat and Temperature Heat and temperature Insulation Science skills: Estimating measuring Predicting By the end of this unit you should know: The difference between heat and temperature. How to measure the temperature. Things will either warm up or cool down to match the temperature of their surrounding Substances are different in their conducting and insulating properties. 72

2 Make a mind map! Write as much as you know, even draw, about the words HEAT and TEMPERATURE. HEAT TEMPERATURE 73

3 4.14.1, Physical science Activity: Heat and temperature Is it hot or not? Collect three bowls of water; fill the first one with warm water, the second one with tap water. Fill the last bowl with ice cold water. Predict which bowl is the coldest. How do you know? Test each bowl carefully with your hands. Were you right? Put the bowls starting with the hottest. We use our sense of touch to find out how hot our surrounding is. You can feel the temperature of water because the heat flows from the three bowls to your hand. Heat is a flow of energy from warmer matter to cooler matter. Now put one hand in the iced water, and the other hand in the warm water, keep them there for a about a minute. Take them out and put your both hands in the third bowl. Discuss how you feel? 74

4 We feel the heat with our hand but sometimes our senses can be fooled! Have you ever felt that you didn t need a jacket, and then when you went outside you were wrong! Sometimes we need to know the exact temperature of things. To measure the temperature accurately we use a thermometer. Many thermometers are made of glass tubes. At the bottom of the tube is a wider part called the bulb. The bulb is filled with a liquid. Some liquids that can be used are mercury ( this is not allowed in schools as it is very dangerous) or colored alcohol. When the bulb is heated, the liquid in the bulb expands, or gets larger. It rises in the glass tube. When the bulb is cooled, the liquid contracts, or gets smaller. It falls in the tube. On the sides of the thermometer are a series of marks. You read the temperature by looking at the mark on the tube where the liquid stops. This is a regular thermometer and it is used in many ways 75

5 Temperature is usually measured on two scales. They are the Fahrenheit scale and the Celsius scale. Activity: Predict the temperature of each bowl. Check your predictions by using a thermometer. Record your results in the table. How close were your estimates? Bowl Warm water Tap water Cold water Estimated Temperature What YOU think! Measured temperature Actual temperature Temperature is a measure of how hot or cold something is. Measuring temperature The temperature can be estimated using our sense of touch. In order to measure the temperature accurately we use the thermometer. 76

6 Types of thermometers: Clinical thermometers: The clinical thermometers are used to measure the body temperature of the patient like: Ear thermometer Underarm thermometer Oral thermometer Food thermometers: There are many food thermometers like: Dial oven-safe thermometers digital instant thermometers Outdoor thermometers: The outdoor thermometers are used to measure the temperature of the surrounding air. 77

7 Flow of Heat Don t let it get cold 1. Imagine a hot dinner on a cold day. What happens to it if you don t eat it straight away? 2. Imagine a cold drink on a hot day. What will happen to it if you leave it for a long time before you drink it? Does the temperature of something hot or cold change to be more like the temperature of its surrounding? Activity: You will need: 3 thermometers A bowl of iced water A bowl of tap water A bowl of warm water 78

8 Steps: 1. Firstly measure and record the temerature of the room. Room temperature 2. Estimate and then measure the temperature of the water in each of the three bowls. Record your measurements. 3. What do you predict the temperature of the water in the three bowls will be in one hour s time? Explain your prediction. Bowl Iced water Tap water Warm water Estimated temperature Measured temperature Temperature after 10 min. Temperature after 20 min. Temperature after 30 min. 4. Leave the bowls for 10 minutes. Measure the temperatures again and after 20 minutes and 30 minutes. 79

9 What do you notice? Can you explain what happened? What do you notice about the temperature of the bowls and the room? Anything that is at a different temperature from its surrounding will change temperature over time. If left long enough, it will either warm up or cool down to match the temperature of all other things around it, including the air. Both the hot dinner and the cold drink will end up at the temperature of the surrounding air. 80

10 Activity Fix a thermometer outside decide with your teacher where. Measuring the temperature during the day and complete the table: Time Temperture outside 7am 9am 11am 1pm 2pm Use the data and plot a graph. Join the lines making a curve. Questions: When was the temperature is highest during the day (24 hours)? Temp Why do you think it was the highest at that time? Time 81

11 Key words: Heat Temperature Thermometer Degrees Celsius Fahrenheit Surrounding Room temperature Key ideas: How hot or cold something is, is called temperature. We can measure the temperature using a thermometer. Heat, a flow of energy from warmer matter to cooler matter. Over time, every material will become the same temperature as its surrounding. Key questions: 1. What is the difference between heat and temperature? Explain why energy flows from the outside air into the inside of a refrigerator

12 3. Look at the following picture below. What will happen to the temperature after (1) hour? The temperature of the juice will be: a) The same temperature b) The room temperature c) Increased over time 20 C 4. Look at the thermometer. Write the temperature it shows in C. 83

13 Physical science Insulation All cups have hot liquid in it. Which cup would you prefer to hold? And why? Discuss. Think carefully about this one! Materials that allow heat to pass through them easily are called thermal conductors. Metals and glass are good thermal conductors. Some materials do not conduct heat well. They are called thermal insulators. Materials such as plastics, wood, wool and air are good thermal insulators. 84

14 Thermal insulator A thermal insulator is a material that does not allow heat to travel through it easily. Which of these spoons do you think will be a good thermal insulator? Metal spoon Wooden spoon Plastic spoon A saucepan of hot water Think What does the handle of each spoon feel like when they have been standing in the hot water for 10 minutes? 85

15 Activity You will need Three cups made from different materials (plastic-glassmetal), thermometers, and hot water. Steps: 1. Fill the cups with hot water. 2. Measure the temperature of the cups. 3. After 15 minutes measure the temperature again. 4. Record your results what do you observe Cup Plastic Glass Metal Temperature Temperature after 15 minutes Which material would you choose for a cup of tea? Why? Insulation Activity You will need: 3 identical cups (with covers). kettle (for boiling water your teacher will pour the hot water for you), 3 thermometers, 3 different types of materials (bubble wrap, foil, paper, elastic bands). 86

16 What do you need to keep the same? In order to make it a FAIR test Wrap each cup with ONE of the materials, use elastic bands to help you.put the lid, on make sure you have a hole to put the thermometer through. Record the temp every minute for 13min. This is the same experiment as yours. Here they are using metal cups and digital thermometers, you can see the different insulation they are using. Material Time (mins) Foil Paper Bubble Wrap 87

17 Think about it? Five glasses containing water at 60 C were each wrapped in a different material. After 10 minutes, the water temperature in each glass was recorded. The results are shown in the table below. Which material would you choose to wrap around a water pipe in winter to stop the water from freezing? Explain why? Some materials conduct heat very well. Think of a metal spoon that has been left in a steaming cup of coffee-it gets very hot! Metals are materials that conducts heat well. Saucepans are made from metals: they heat up quickly. However the handles are usually made from another material Such as plastic or wood, because they are insulators. 88

18 Project: What s the problem with getting ice-cream home from the shops in the summer? Yes, it nearly always starts melting before you can get to the freezer. Your challenge is to design some kind of packaging or bag that will keep ice-cream cold for enough time to get home from the shops. You will make your design in school. What I will need: What I will do: Why I think it will work: Explain why some materials keep foods cool and others don t. 89

19 Key words: Thermal conductor Thermal insulator Conduct Insulate Key ideas: Materials that allow heat to pass through them easily are called thermal conductors. Materials do not conduct heat well are called thermal insulators. Key questions: 1. What do we call materials that do not let heat pass through them? Salman bought a flask. Which of these are true and which are false? a. The flask will only keep drinks hot. True / False b. The flask will keep cold drinks cold. True / False c. The flask will not keep cold drinks cool. True / False d. The flask will keep hot drinks hot. True / False 90

20 3. Sara is cooking some rice at home. She puts water into a metal pan and places the pan on the cooker. Why is metal a good material for the pan? 4. Look at the graph and answer these questions. a. Which cup kept the liquid warmest?... d. Which cup is the best thermal insulator?... c. What do you think was the temperature of the room?... 91