Subjective Questions
1. List the various types of simple machines and their uses.
Simple machines: Lever, Pulley, Wheel and axle, Inclined plane, Screw, Wedge.
Uses:
1. Lever – Used to lift or move objects by changing magnitude and direction of force.
2. Pulley – Used to lift heavy objects.
3. Inclined plane – Used to lift loads easily.
4. Screw – Used to hold things together or lift heavy objects.
5. Wedge – Used to cut or split things.
6. Wheel and axle – Used to move or turn objects (e.g., carts, doorknobs).
Uses:
1. Lever – Used to lift or move objects by changing magnitude and direction of force.
2. Pulley – Used to lift heavy objects.
3. Inclined plane – Used to lift loads easily.
4. Screw – Used to hold things together or lift heavy objects.
5. Wedge – Used to cut or split things.
6. Wheel and axle – Used to move or turn objects (e.g., carts, doorknobs).
2. Compare Class I and Class II levers.
- Class I lever:
i) Fulcrum is between effort and load (e.g., scissors, crowbar).
ii) Mechanical advantage can be greater, less, or equal to 1.
- Class II lever:
i) Load is between fulcrum and effort (e.g., wheelbarrow, nutcracker).
ii) Mechanical advantage is always greater than 1.
i) Fulcrum is between effort and load (e.g., scissors, crowbar).
ii) Mechanical advantage can be greater, less, or equal to 1.
- Class II lever:
i) Load is between fulcrum and effort (e.g., wheelbarrow, nutcracker).
ii) Mechanical advantage is always greater than 1.
3. Distinguish between a single fixed pulley and a single movable pulley.
- Single fixed pulley:
i) Changes direction of force.
ii) Mechanical advantage = 1.
iii) Effort applied opposite to direction of load movement.
iv) Axle is fixed to rigid support.
- Single movable pulley:
i) Reduces effort needed.
ii) Mechanical advantage = 2.
iii) Effort applied in same direction as load movement.
iv) Axle is not fixed.
i) Changes direction of force.
ii) Mechanical advantage = 1.
iii) Effort applied opposite to direction of load movement.
iv) Axle is fixed to rigid support.
- Single movable pulley:
i) Reduces effort needed.
ii) Mechanical advantage = 2.
iii) Effort applied in same direction as load movement.
iv) Axle is not fixed.
4. Explain the wheel and axle arrangement with its types.
A wheel and axle consists of a circular wheel connected to a cylindrical rod (axle).
Types:
i) Force applied on wheel → wheel turns axle (used in doorknobs, screwdrivers, taps).
ii) Force applied on axle → axle turns wheel (used in ferris wheels, bicycle pedals, fans).
Types:
i) Force applied on wheel → wheel turns axle (used in doorknobs, screwdrivers, taps).
ii) Force applied on axle → axle turns wheel (used in ferris wheels, bicycle pedals, fans).
5a. Why should moving parts of machines be oiled or greased?
Oiling reduces friction, prevents wear and tear, and increases efficiency.
5b. Why should non-moving parts of machines be painted or oiled?
Painting or oiling prevents rusting and corrosion, increasing the machine’s life.
Exemplar Problems
1a. For Class III levers, the mechanical advantage is always less than 1. Why?
In Class III levers, effort arm is shorter than load arm, so mechanical advantage is always less than 1.
1b. If there is no advantage, why are Class III levers useful?
They allow application of effort over a greater distance and provide speed and accuracy (e.g., broom, cricket bat).
2. An electric fan is a complex machine. Where would you find:
a. an inclined plane?
b. a wheel and axle?
a. an inclined plane?
b. a wheel and axle?
a. The fan blades act as inclined planes since they are slanted surfaces.
b. The motor shaft and blades act as wheel and axle.
b. The motor shaft and blades act as wheel and axle.
3. Shoelaces are like the rope on a pulley system. Explain.
Like a pulley rope, shoelaces help tighten shoes by pulling and distributing force efficiently.
4. Which simple machine would you use:
a. to open a door?
b. to get a big rock off the road?
c. to chop vegetables?
a. to open a door?
b. to get a big rock off the road?
c. to chop vegetables?
a. Lever (door handle).
b. Lever (crowbar).
c. Wedge (knife).
b. Lever (crowbar).
c. Wedge (knife).
