1. Sun is very hot because there is a lot of burning of matter on the star Sun. A nuclear fission chain reaction happens on the surface of Sun. The heat produced from the nuclear reaction makes Sun red hot and some energy is emanated in the form of radiation. This radiation carries a lot of energy. That hits us and heats up our bodies and the atmosphere.
There is a lot of electromagnetic radiation in the visible range. That radiation falls in the range of color red. Also, the color red is not scattered much. The other colors are scattered a lot. So sun appears red. Otherwise Sun could appear as a bright white circular disc.
2. Moon is a planet and is like Earth - in receiving light and energy from Sun.
Moon receives radiation during the day on moon and then in the night, the energy is radiated back in to the atmosphere. So moon remains cool.
3. Speed = the distance travelled by a body in unit time.
= distance / time duration
= length of the path traced by an object or a person in one second.
4. scalar quantity is a physical quantity which has only a magnitude and value. It does not have a direction. A scalar quantity has units and dimensions.
Examples are: number of people. Speed of light. Temperature.
Vector quantity is a physical quantity which has a magnitude as well as a direction. Vectors follow the vector law of addition. They follow the parallelogram law of vector addition or subtraction.
Vector in a direction is different from a vector in another direction even though both have the same magnitude.
displacement, force, acceleration, velocity, torque
5. uniform speed
If a body covers travels moves equal distances in equal intervals of time, then it is moving with a uniform speed. ie., constant speed.
non uniform speed
if a body travels unequal distances in equal intervals of time, then it is moving with a non uniform speed.. it is variable speed.
6. mass is the amount of matter in a body or object or person.
It is a collection of particles that belong to the body. Mass is a physical quantity and its unit of measurement is kg.
weight W is the force with which the Earth attracts a body of mass m towards its center. The force is the Newtons' gravitational force of attraction. Weight depends on the acceleration due to gravity at that location on Earth. Mass is independent of location of the object. Weight has a direction - towards the center of Earth.
Weight depends on the mass of the body. Weight is usually expressed in terms of mass, ie., W = m * g. When only mass is specified, it means that we should multiply with g to get the weight in terms of force units..