machines 2024-25

## Machines - **

Definition**: A piece of equipment with moving parts designed to perform a specific job. Machines typically require energy sources such as electricity, gas, or steam to function. -

**Physics Definition**: A mechanical device that converts input work into output work. - **Types of Simple Machines**: There are six common simple machines: - Lever - Wheel and axle - Pulley - Inclined plane - Wedge - Screw ## Functions and Uses of Simple Machines 1. **Force Multiplier**: Machines allow lifting heavy loads with less effort. - **Examples**: Jacks, spades, pulleys, wheelbarrows. 2. **Changing Point of Effort Application**: Machines can change where effort is applied. - **Example**: Rear wheel of a bicycle is rotated by pedaling. 3. **Changing Direction of Effort**: Machines can alter the direction in which effort is applied. - **Example**: Single fixed pulley used to raise water. 4. **Gain in Speed**: Machines can facilitate faster movement of a load with less movement of effort. - **Examples**: Scissors, ice tongs. ## Technical Terms Related to Machines - **Load (L)**: The resistive force to overcome. - **Units**: SI: Newton, CGS: dyne. - **Effort (E)**: The force exerted on the machine. - **Units**: SI: Newton, CGS: dyne. - **Mechanical Advantage (M.A.)**: Ratio of load to effort. - **Formula**: M.A. = Load / Effort. - **Unit**: No unit. ### Values of Mechanical Advantage 1. **M.A. > 1 (Force Multiplier)**: Machine requires less effort than load. - **Example**: A jack. 2. **M.A. < 1 (Gain in Speed)**: More effort is needed than the load. - **Example**: Scissors. 3. **M.A. = 1 (Change Direction)**: Used to change the direction of effort with no gain in force or speed. - **Example**: Single fixed pulley. ## Velocity Ratio (V.R.) - **Definition**: Ratio of the velocity of effort to the velocity of load. - **Formula**: V.R. = Velocity of Effort / Velocity of Load. - **Values of Velocity Ratio**: 1. **VR < 1**: Gain in speed. 2. **VR > 1**: Force multiplier. 3. **VR = 1**: Change direction of effort. - **Unit**: No unit. ## Work Input and Output - **Work Input**: Work done on the machine by effort. - **Formula**: Work Input = Effort * Displacement of Effort. - **Work Output**: Work done by the machine on the load. - **Formula**: Work Output = Load * Displacement of Load. - **Efficiency (η)**: Ratio of work output to work input. - **Formula**: Efficiency = (Work Output / Work Input) x 100%. ## Principle of a Machine - **Effort Point**: Where work is applied to the machine. - **Load Point**: Where work is performed on the load. - **Ideal Machine**: Perfect energy transfer with 100% efficiency (no energy loss). - **Actual Machine**: Output energy is less than input due to various losses (friction, inelasticity, etc.). ## Relationship Between Efficiency, Mechanical Advantage, and Velocity Ratio - **Formulae**: - Efficiency (η) = Work Output / Work Input. - η = M.A. / V.R. - M.A. = V.R. x η. ## Levers - **Definition**: A bar that pivots around a fixed point (fulcrum). - **Principle**: At equilibrium, the moments of the load and effort around the fulcrum are equal. - **Formula**: Load x Load Arm = Effort x Effort Arm (L x LA = E x EA). ### Types of Levers 1. **Class I Levers**: Fulcrum is between effort and load (e.g., seesaw, scissors). - M.A. and V.R. can be >1, <1, or =1. 2. **Class II Levers**: Load is between effort and fulcrum (e.g., nutcracker, bottle opener). - M.A. and V.R. > 1. 3. **Class III Levers**: Effort is between load and fulcrum (e.g., fire tongs, fishing rod). - M.A. and V.R. < 1. ## Examples of Levers in Human Body 1. **Class I**: Nodding head (spine as fulcrum). 2. **Class II**: Rising on toes (toes as fulcrum). 3. **Class III**: Lifting load with forearm (elbow as fulcrum). ## Pulleys 1. **Fixed Pulley**: Axis is stationary (changes direction of effort). 2. **Movable Pulley**: Axis is movable (provides mechanical advantage). ### Mechanical Advantage and Efficiency of Pulleys - **Single Fixed Pulley**: MA = 1, VR = 1, Efficiency < 100%. - **Single Movable Pulley**: MA = 2, VR = 2, Efficiency = 100%. - **Combination of Pulleys**: MA can increase by using multiple pulleys. ## Multiple Choice Questions & Concepts - Review questions related to levers, mechanical advantage, efficiency, and definitions of machines for understanding key concepts.