# Forces (Moments, Hooke's Law, Mechanical Quantities)

- Created by: Jasmine Tw
- Created on: 25-04-22 18:53

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- FORCES
- MECHANICAL QUANTITIES
- Vector
- Magnitude and direction
- e.g. velocity, force, displacement

- Scalar
- Magnitude only
- e.g. time, distance, seed

- Centre of mass
- The single point where an object's weight is said to act

- Resultant force
- sum of all forces in all directions acting on an object
- found by adding/subtracting forces acting along a straight line

- Weight
- larger the mass, stronger the field, greater the attraction
- measured by a newton meter/calibrated spring-balance
- gravitational attraction
- W=mg
- g=0.8 N/kg on Earth

- Vector
- HOOKE'S LAW
- Elastic potential energy
- Ee = ½ ke^2
- 1 J = 1 Nm

- W=Fs
- also applies to compression

- Ee = ½ ke^2
- Force is proportional to extension up to the limit of proportionality
- F = ke
- e = extension (m)
- k = spring constant (Nm^-1)

- Deformity
- Elastic deformity
- return to original shape when load removed

- Plastic deformity
- Does not return to original shape when load removed
- spring is pulled too far

- Does not return to original shape when load removed
- changing shape

- Elastic deformity

- F = ke
- Work done
- against friction, causes increase in temp. of object
- Work is done when a spring is stretched/ compressed
- more than one force is applied

- when energy is transferred from object doing the work to another form

- Elastic potential energy
- Moments
- turning effect of a force around a pivot
- M = Fd
- d is perpendicular to the line of action (m)
- M = moment (Nm)
- clockwise moment = anticlockwise moment

- M = Fd
- Equilibrium
- clockwise moment = anticlockwise moment

- Gears
- Alter force + speed
- High gear
- Large gear drive small gear
- rotates faster & smaller moment

- Large gear drive small gear
- Low gear
- Small gears drive large gears
- Large gears rotate slowly & larger moment
- force applied is further away from pivot
- momentum of large gear is greater

- force applied is further away from pivot

- Large gears rotate slowly & larger moment

- Small gears drive large gears

- Levers
- act as force multiplier
- make up by load, effort, pivot
- increases a provided force
- effort to pivot > pivot to load
- force applied on load is greater to reach equilibrum

- turning effect of a force around a pivot

- MECHANICAL QUANTITIES

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