Science · Class 8
Force and Pressure
Force, pressure in fluids, and atmospheric pressure.
4 sections15–25 min read6 MCQs · 2 examples
Chapter Overview
Pressure = Force / Area. SI unit: pascal (Pa). 1 Pa = 1 N/m².
Force is a push or pull that can change motion or shape. Pressure is force per unit area. This chapter covers contact and non-contact forces, atmospheric pressure, and liquid pressure.
Force
- SI unit: newton (N); measured by spring balance
- Contact forces: friction, muscular
- Non-contact: magnetic, electrostatic, gravitational
- Net force changes state of motion
Pressure
- Pressure = Force / Area (P = F/A); SI unit pascal (Pa)
- Sharp knife: small area → high pressure
- Broader straps reduce pressure on shoulders
Atmospheric Pressure
- Air has weight — presses from all sides
- 760 mm Hg at sea level ≈ 1 atm
- Drinking straw, rubber sucker use atmospheric pressure
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Pressure calculation
Force 100 N on area 0.5 m². Find pressure.
- 1P = F/A = 100/0.5
- 2P = 200 Pa
Answer
200 Pa
Atmospheric pressure
Why does liquid rise in drinking straw?
- 1Sucking reduces pressure inside straw
- 2Atmospheric pressure pushes liquid up
- 3Pressure difference
Answer
Atmospheric pressure pushes liquid up
Key Points to Remember
- ✓ Liquids exert pressure — increases with depth
- ✓ Dam walls thicker at bottom
- ✓ High altitude: lower atmospheric pressure
Exam Tips
- • Calculate pressure from F and A
- • Give examples of high and low pressure
- • Explain working of rubber sucker
Practice MCQs — Force and Pressure
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Question 1 of 6Score: 0/0
SI unit of force is: