Mechanical Components and Devices (Core) Flashcards
What are the two types of motion in a product?
Hidden motion, eg in a sewing machine, and visible motion, eg in scissors.
What are the principles of mechanical systems?
For products to move and give an output motion, a force or an input motion is required, eg squeezing scissor handles is needed to push the blades together, cutting the material. Forces don’t just push - they can twist or pull as well. These forces are measured in units called Newtons (N). The size of a force or motion always affects the output.
What is the input, process and output in a bike?
- Input - the force applied to the pedals by the cyclists’s feet.
- Process - the chain turns the gear system, converting the energy produced.
- Output - the wheels turn and the bike moves.
How does force affect distance?
If a cyclist is pushing with 150W of power when cycling uphill, it is the same power as 150W when cycling on flat ground. Although 150W of power is the same no matter what the gradient, the 150W for uphill cycling feels harder and, as such, the speed of travel can change and less distance will be covered due the force of gravity.
What are the four types of motion?
- Rotary - motion moves in a complete circle, eg a wheel turning. Rotational speed is found by dividing the number of revolutions by the time it takes.
- Linear - motion moves in a straight line, eg a train on a track. Linear speed is found by dividing the distance travelled by the time it takes.
- Oscillating - motion moves backwards and forwards in part of a circle, eg a pendulum of a mechanical clock. To be oscillating, the motion must be repetitive. Measured in oscillations per second or minute.
- Reciprocating - motion moves backwards and forwards in a straight line, eg a piston or pump. Measured also in oscillations per second or minute.
What is a pulley?
A wheel with a grooved edge that a cord passes around. They use mechanical advantage (the ratio of force produced compared to force applied) , to lift up loads. They can be used by hand or attached to a motorised winch (a machine that lifts heavy loads by turing a rope or chain around a circular drum) to increase the amount of weight that can be lifted. They are a simple and manouverable way to move large objects.
What mechanical advantage do pulleys provide?
The mechanical advantage is equal to the number of sections (U-shaped) of rope pulling up on the object.
What do belt drives do?
They transfer movement from one rotating pulley to another, each held on a shaft, and are typically make from a soft, flexible material such as rubber. Grooves on the belts help them to grip and turn.
What are some examples of mechanisms that are belt-driven?
Winches, treadmills and washing machines.
How do you calculate velocity ratio in a belt drive?
Diameter of the driven pulley ÷ diameter of the driver pulley
How do you calculate the output speed in a belt drive?
Input speed ÷ velocity ratio
What is a gear?
A wheel with teeth that can change the speed/direction of a movement.
What is a gear train?
Two or more gears interlocking together.
How do you calculate the gear ratio in a gear train?
Number of teeth on driven gear ÷ number of teeth on the drive gear
What is the name of the middle gear in a gear train that lets two gears move the same way?
The idler.
