Keywords
Balanced force: forces of equal magnitude applied in opposite directions are called balanced forces.
Unbalanced force: forces of unequal magnitude applied in opposite directions are called unbalanced forces.
Contact forces: forces that exist between objects that are directly or indirectly in physical contact with each other are called contact forces.
Non-contact forces: forces exist between objects that are not in contact with each other
Frictional force: a force that acts on every object from the opposite direction to that of motion is called frictional force.
Electrostatic force: the force that acts between charge-carrying objects is called electrostatic force.
Gravitational force: the attractive force of Earth is called gravitational force.
Point of contact: the point where force is applied is called the point of contact.
Thrust: perpendicular force acting on an object is called thrust.
Pressure: thrust acting on per unit of an area is called pressure.
Atmospheric pressure: the pressure exerted by the atmosphere on different things is called atmospheric pressure.
Manometer: a device used to measure pressure.
Barometer: a device used to measure atmospheric pressure.
Exercise
A. Tick (✔) the correct options.
1. Which of these is not a characteristic of force?
a) Magnitude
b) Direction
c) Height
2. What is the name given to the point where force is applied?
a) Point of contact
b) Point of force
c) Point of pressure
3. What is the branch of science that studies frictional force called?
a) Biology
b) Tribology
c) Frictionology
4. Which of these forces only attracts?
a) Gravitational
b) Electrostatic
c) Magnetic
5. How many Pascals are equal to 1 N/m²?
a) One
c) Hundred
b) Ten
6. What type of relation exists between pressure exerted on a body and surface area?
a) Direct
b) Inverse
c) No relation
Match the columns
| A | B |
|---|---|
| 1. Force | a.Non-contact force |
| 2. Pressure | b.Otto von Guericke |
| 3. Barometer | c.Pascal |
| 4. Magnetic force | d.Newton |
| 5. Manometer | e.Contact |
| 6. Muscular force | f.Atmospheric pressure |
Answer 1-d, 2-c, 3-f, 4-a, 5-b, 6-e
C. Fill in the blanks.
1. Force is defined as a ………. or………..
2. ……….force acts in the direction opposite to the direction of motion.
3. The force exerted by a charged body on another charged or uncharged body is called ………..
4. There exists a ……….. relationship between thrust acting on a body and pressure exerted on it.
5. The pressure exerted by a liquid ……….. with increases in depth.
6. The S.I. unit of force is ………
Answer 1. push or a pull, 2. Frictional, 3. electrostatic force, 4 . 5. increase, 6. newton
Numerical questions
1. An iron box has dimensions of 75cm×30cm×15 cm. Calculate the pressure exerted by the iron box on the soil, if a force of 7.5 N is applied when it is placed on
a) 75cm×30 cm as base
b) 30cm×15 cm as base
2. The tip of a pin has an area of 0.00001m². Calculate the pressure exerted by it if the force applied is 10 N.
3. A force of 800 N exerts pressure on an area of 40 cm2. What pressure do they exert on the floor?
4. In a tug of war the members of Team A pull with a force of 100 N, 115 N, and 125 N. Team B pulls with a force of 105 N, 128 N, 107 N. What is the resultant force?
5. Calculate the pressure when a force of 5 N is applied on an area of 5 sq. cm.