One calorie is the amount of heat energy required to raise the temperature of 1 gram of water through 1°C

The form of heat transfer from places of high temperature to places of low temperature by the actual movement of molecules is called convection. Convection takes place in liquids and gases.

Three types ofheat transfer:
(i) Conduction
(ii) Convection
(iii) Radiation.

Effects of heat:
When heat energy is supplied to any substance, it brings about many changes.
The three important changes are:
(i) Expansion
(ii) Increase in temperature
(ii) Change in state.

Thermos flask:
The thermos flask is an insulating storage vessel that keeps its content hot cooler than the surroundings for longer time.

Working:
(i) A thermos flask has double wails, which are evacuated.
(ii) It is silvered on the inside.
(iii) The vacuum between the two walls prevents heat being transferred from the inside to the outside by conduction and convection.
(iv) with very little air between the walls, there is almost no transfer of heat from the inner wall to the outer wall or vice versa inner wall to the outer wall or vice versa 
(v) Conduction can only occur at the points where the two walls meet, at the top of the bottle and through an insulated support at the bottom
(vi) The silvered walls reflect radiated heat buck to the liquid in the bottle.

Thermostat.
(i) A thermostat is a device which maintains the constant. temperature of a place or an object
(ii) The word thermostat is derived from two Greek words, thermo, meaning heat and 'static' meaning staying the same.
(iii) Thermostats are used in any device or system that gets heated or cools down to a pre-set temperature 
(iv) It turns an appliance on or off when a particular temperature is reached.
(v) Sometimes, a thermostat functions both as the sensor and the controller thermal of a system.
(vi) Examples for thermostats include building heater, central heater in a room, air conditioner water heater, as welt as kitchen equipments including oven and refrigerators.

When a lake freezes, the upper layer freezes due to being in contact with the cold atmosphere. This ice sheet doesn't sink as it is less dense than water. Once frozen, the ice sheet acts as an insulator and it insulates the water at the bottom from cooling and freezing. It keeps the water inside warm enough to be in a liquid form.