We obtain antibiotics and vaccines from microbes.
Antibiotics:
The word 'Anti' means against. Antibiotic is a substance produced by living organisms which is toxic for other organisms. Sir Alexander Fleming was the first person to discover the antibiotic penicillin in the year 1928. The antibiotic penicillin was obtained from the fungi penicillium chrysogenum. It is used to treat disease such as tetanus, diphtheria, antibiotic streptomycin is obtained from Streptomyces bacteria to cure various bacterial infections eg, Plague.
Vaccines:
Vaccines are prepared from dead or weakened microbes - Edward Jenner was the first person to discover small pox vaccine. He coined the term vaccination. When the vaccine is injected to the body of a patient, the body produces antibodies to fight against the germs. These antibodies remain inside the body and protects from future invasion of the germs. Therefore vaccination is otherwise called as immunization.
Eg: MMR vaccine for measles, Mumps, Rubella.
BCG (Bacille Calmette Guerin) vaccine for tuberculosis.

Images formed by a concave mirror.

(i) Using lubricants:
1. A substance, which reduces the frictional force is called a lubricant. Eg grease, coconut oil, graphite, castor oil etc.
2. The lubricants fill up the gaps in the irregular surfaces between the bodies in contact
3. This provides a smooth layer thus preventing a direct contact between their rough surface.
(ii) Using ball bearing:
1. Since the rolling friction is smaller than sliding friction, sliding is replaced by rolling with the usage of ball bearings.
2. Lead shots in the bearing of a cycle hub reduces the friction.

Types of Friction:
Friction can be classifed into two basic types
I Static friction
II. Kinetic friction
I. Static friction:
The friction experienced by the bodies which are at rest is called static friction.
eg:- a knot in a thread.
II. Kinetic friction:
Friction existing during the motion of bodies is called kinetic friction
Kinetic friction can be classified into two types
(i) Sliding friction
(ii) Rolling friction
(i) Sliding friction:
When a body slides over the surface of another body, the friction acting between the surfaces in contact is called sliding friction
eg: Sliding on snow in a sled.
(ii) Rolling friction:
When a body rolls over another surface, the friction acting between the surfaces in contact is called rolling friction.
eg: Wheels in vehicles, trolleys, Suitcases.

Speed of light in air (C) = 3 x 10⁸ ms^-1
Refractive index (μ) = 1.5
Refractive index (μ) = \(\frac { Speed\ of\ light\ in\ air(c) }{ Speed\ of\ light\ in\ medium(v) } \)
Speed of light in the medium (v) = \(\frac { Speed\ of\ light\ in\ air(c) }{ Refractive\ index(\mu ) } \)
V = \(1.5 = \frac { 3 \times { 10 }^{ 8 } }{ v } = \frac { 3 \times { 10 }^{ 8 } }{ 1.5 }\)
v = 2 x 10⁸ ms^-1
Speed of light in the medium (v) = 2 x 10⁸ ms^-1