Thursday, 31 July 2014

Think 4

Cold water's temperature increase while hot water's temperature decrease. 
The rate of increase/decrease is different. The rate of decrease is faster than the rate of increase as metal is a better thermal energy conductor, causing thermal energy to be lost to the cold water at a faster rate. The upper curve showed faster rate of flow of TE.

Why is metal and styrofoam cup used respectively? 
MetalCup---Allow speedier transfer of thermal energy from the hot water to the cold water so as to speed up the rate of thermal energy gain and loss

StyrofoamCup---Reduce(not prevent)the cold water from gaining heat from surroundings. This ensure that room temperature does not play as a factor to affect the experiment. 

When the question is little open, you need to make assumptions so that you can narrow the possibilities.

The hot water is losing TE from the room temperature and the cold water. Visa Versa; the cold water is gaining TE from the room temperature and the hot water. In other words, using styrofoam cup help eliminate the room temperature.

Think 3

Tiles are better thermal conductors than parquet {1st point}
Explain what a better thermal conductive is? {2nd Point}
Answer: The material which remove TE from your feet at a faster rate. 

 Thinking Process:
Room Temp: 28degrees (linked to the temp of flooring)
Body Temp:  37degrees

Tiles feel cold because there is a greater difference between your body temperature and the room temperature than parquet causing thermal energy to be removed at a faster rate.  

Saturday, 26 July 2014

Question: (Describe Graph Shape)


The graph shows a smooth curve decreasing from 85degrees to room temperature. 
(Water lost thermal energy to cooler surroundings) 
In the first 40mins, the temperature decreased steeply due to the big difference in the temperature of the water and the room temperature.
For the next 30mins,  when the temperature neared 30degrees, the decrease in temperature is less steep as the temperature of the water and the room temperature are reaching an equilibrium.

Think 2

QUESTION: KEYWORDS: shiver, feel cold

My Answer:
When you come out of the pool, water on your body evaporates. At the same time, taking Thermal energy away from your body. On a hot day, the surroundings have more thermal energy, thus, increasing rate of evaporation of the water on your body while taking away more Thermal energy from your body. When your body has less Thermal energy, the molecules will move slower, causing a drop in temperature, making our body feel cold. 

Standard 2mark answer: (KeyPoints)
-(Why do you feel cold):  
When I come out of the water, the water droplets on my body evaporate, at the same time, taking heat away from the body. When my body lose thermal energy, I feel cold. 
-(Why do you shiver):      
As the water evaporates, there is a change of state from liquid to gas. This change of state requires a lot of thermal energy. As more thermal energy is removed from my body within a shorter period of time, I shiver.

WHY DO WE SHIVER? (At Micro-Level)
The human body needs to stay at the same temperature(37degrees Celsius) to survive. When you feel cold, sensors in your skin send messages to your brain telling you a need to warm up. Your brain then sends messages to nerves, telling your muscles to tighten and loosen rapidly which is what we call shivering. It does this because when muscles move they generate heat.
When you put towel/go back to the swimming pool, you are preventing water on your body from evaporating. That is why you would stop feeling cold.

Think 1


Concept:   Thermal energy travels from hotter region to colder region. 
My Answer: 
On a hot day, our body(colder region) gain thermal energy from the hot surroundings(hotter region)
Our body has more thermal energy than the air-conditioned surroundings. Therefore when we enter the air-con room,  thermal energy travels from our body to the colder surroundings. When our body lost thermal energy, we would feel cold.

Further Thinking:
Why does our body gain heat from the hot surroundings?

Human body maintains at a internal temperature of 37°C. Variations, usually of less than 1°C, occur with the time of the day, level of physical activity and emotional state. A change of body temperature occurs only during illness or when environmental conditions are more than the body's ability to cope with extreme heat.
As the environment temperature increases, the body temperature increases. The body's internal "thermostat" maintains a constant inner body temperature by pumping more blood to the skin and by increasing sweat production. In this way, the body increases the rate of heat loss to balance with the heat gain. In a very hot environment, the rate of "heat gain" is more than the rate of "heat loss" causing body temperature to rise. A rise in the body temperature results in heat illnesses.

3Main Ideas need to be included:
-Why you feel cold?
You lose thermal energy

Why your body lose thermal energy?
-(Concept) Thermal energy travels from a hotter region to a colder region.
Hotter Region--Body
Colder Region--AirCon Room

- "Hot Day"must show relevance to answer
On a hot day, our bodies gain thermal energy from the hot surroundings

Notes from Class Discussion:
-Don't use atoms/particles in physics. Correct term is molecules when you are talking about something at the micro level.
-It is your choice to decide on macro/micro
-Use the term "Thermal Energy" not heat