The net force is defined as is the sum of all the forces acting on an object. Net force can accelerate a mass. Some other force acts on a body either at rest or motion. The net force is a term used in a system when there is a significant number of forces.  

The antibodies destroy the antigen (pathogen) which is then engulfed and digested by macrophages. White blood cells can also produce chemicals called antitoxins which destroy the toxins (poisons) some bacteria produce when they have invaded the body. Antibodies are proteins produced by the body to neutralize or destroy toxins or disease-carrying organisms. Antibodies are disease-specific. For example, measles antibody will protect a person who is exposed to measles disease, but will have no effect if he or she is exposed to mumps.

The postulates of this theory may be stated as follows:

• Matters are composed of very tiny particles called atoms.
• These particles are too small to see and cannot be created or destroyed in a chemical reaction.
• Atoms of a specified element are identical in mass and chemical properties.
• Atoms of different elements have different masses and chemical properties.
• Atoms combine in the ratio of small whole numbers to form compounds.
• The relative number and kinds of atoms are constant in a given compound.

There are five basic laws of chemical combination that govern the chemical combinations of elements:

1. Law of Conservation of Mass

In simple terms, this law states that matter can neither be created nor destroyed. In other words, the total mass, that is, the sum of the mass of reacting mixture and the products formed remains constant. Antoine Lavoisier gave this law in the year 1789 based on the data he obtained after carefully studying numerous combustion reactions.

2. Law of Definite Proportions

Joseph Proust, a French chemist stated that the proportion of elements by weight in a given compound will always remain exactly the same. In simple terms, we can say that irrespective of its source, origin or its quantity, the per cent composition of elements by weight in a given compound will always remain the same.

3. Law of Multiple Proportions

This law states that if two elements combine to form more than one compound, the masses of these elements in the reaction are in the ratio of small whole numbers. This law was given by Dalton in the year 1803.

4.  Gay Lussac’s Law of Gaseous Volumes

In 1808, Gay Lussac gave this law based on his observations. This law states that when gases are produced or combine in a chemical reaction, they do so in a simple ratio by volume given that all the gases are at the same temperature and pressure. This law can be considered as another form of the law of definite proportions. The only difference between these two laws of chemical combination is that Gay Lussac’s Law is stated with respect to volume while the law of definite proportions is stated with respect to mass.

5. Avogadro’s Law

Avogadro proposed this law in the year 1811. It stated that under the same conditions of temperature and pressure, an equal volume of all the gases contains an equal number of molecules. This implies that 2 litres of hydrogen will have the same number of molecules as 2 litres of oxygen given that both the gases are at the same temperature and pressure.

A sound is a form of energy, just like electricity, heat or light. Let’s examine some sources of sounds like a bell. When you strike a bell, it makes a loud ringing noise. Now, instead of just listening to the bell, put your finger on the bell after you have struck it. Can you feel it vibrating? This is the key to the sound. It is even more evident in guitars and drums. You can see the wires vibrating every time you pluck it. When the bell or the guitar stops vibrating, the sound also stops.

There are many reasons. Some of them are

•To keep the lines equidistant from each other.

•To reduce unwanted vibrations in the track.

•The sleepers have a large surface area compared to the lines; this larger surface area decreases the pressure due to the weight of the train on the track. If only the rails were used without slippers; they being thinner would extent greater pressure over the bed of stone and move deeper in to the ground

1. Tissue that forms the inner lining of our mouth → squamous epithilium
2. Tissue that connects muscle to bone in humans → tendons
3. Tissue that transports food in plants → Phloem
4. Tissue that stores fat in our body → Adipose tissue
5. Connective tissue with a fluid matrix → Blood
6. Tissue present in the brain → Nervous tissue

Fractional distillation is a type of distillation which involves the separation of miscible liquids. The process involves repeated distillations and condensations and the mixture is usually separated into component parts. The separation happens when the mixture is heated at a certain temperature where fractions of the mixture start to vaporize.

CFCs contain both chlorine and fluorine. CFCs are very stable and do not get degraded by any natural process. In the ozone layer present in the outer region of the atmosphere (25-40 km above sea level), CFCs are dissociated by ultraviolet light to release free chlorine atoms. Free chlorine atoms catalyse the breakdown of ozone molecules (03) into oxygen. This results in degradation of the ozone layer. Thinning of the ozone layer would allow penetration of ultraviolet light into Earth’s atmosphere causing blindness, skin cancer and mutations.

Soil pollution refers to the contamination of soil with anomalous concentrations of toxic substances. It is a serious environmental concern since it harbours many health hazards. For example, exposure to soil containing high concentrations of benzene increases the risk of contracting leukaemia.

Some common causes of soil pollution are listed below,

• Improper disposal of industrial waste: industries are believed to be one of the leading causes of soil pollution due to improper management and disposal of the toxic wastes generated during industrial activities.
• Excessive and inefficient usage of pesticides and fertilizers: the agriculture industry makes extensive use of chemical fertilizers and pesticides for the growth and maintenance of crops. However, excessive and inefficient use of these toxic chemicals can seriously contaminate the soil.
• Petroleum or diesel spills: leaks in fuel transportation pipes can cause fuel spills. These fuels are known to contain toxic hydrocarbons which can cause soil contamination.

The branch which deals with the movement of energy from one form to the other and the relation between heat and temperature with energy and work done is called as thermodynamics. In other terms we can define thermodynamics as the science stream that deals with the study of the combined effects of heat and work on the changes of state of matter confined by the laws of thermodynamics. Chemical reactions which releases heat energy associated with it are converted into different usable forms based on the laws of thermodynamics. The fact that energy can only be transformed from one form to the other forms and its use in different industries is on the basis of energy transformation. We are aware that chemical reactions have energy associated with it. The laws of thermodynamics deal with energy changes during a reaction and are not concerned with the rate at which the reaction is proceeding.

Your nails are made of keratin. Keratin is a type of protein that forms the cells that make up the tissue in nails and other parts of your body. Keratin plays an important role in nail health.

Newton used Kepler's third law of planetary motion to guess how the force of gravitation of the earth is weakened by distance. Suppose a planet revolves around the sun in a circular orbit of radius r with speed v, then the force acting on the planet is given by

If T is the period of revolution of the planet around the sun, then its orbital velocity will be

This is inverse-square rule for the force of gravitation. According to this rule, the force of gravitation on a planet should decrease as the square of the distance of the planet from the sun.

Newton further showed that the gravitational force is proportional to the product of the masses of the two objects. Thus, Newton formulated the universal law of gravitation.

Density, mass and volume are all related by the formula,

d = V/m​

where dd is density, VV is volume, and mm is mass. This can be rearranged in order to find volume or mass depending on which quantities you are given and what the question asks you to find. 

Mass is normally measured in grams, g, or kilograms, kg, whereas, volume is normally measured in cubic centimetres, cm³, or cubic metres, m³.

This means when dividing mass by volume, the resulting units are typically grams per cubic centimetre (g/cm³), or kilograms per cubic metre (kg/cm³). These are compound units