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Module 3 - Chapter 4 - Forces in action - Coggle Diagram
Module 3 - Chapter 4 - Forces in action
Force, mass and acceleration
Net force acting on an object will make the object accelerate in the direction of the net force
F = ma
Mass and weight
Mass - How much matter and object contains
Weight - gravitational force acting on the object
W = mg
You can determine weight using a newtonmeter
Free body diagrams
Isolates all the forces acting on a particular object
Representing forces
Arrow length shows magnitude of the force
Arrow direction shows direction of force
Forces drawn to scale with labels
Forces
Weight - gravitational force acting on an object through its centre of mass
Friction - Force that arises when two surfaces rub against eachother, it opposes motion
Drag - Frictional force on an object in a fluid that opposes motion
Tension - Force within a stretched cable or rope
Upthrust - Upward buoyancy force acting on an object when it is in a fluid
Normal contact force - Force arises when one object rests on another object
Drag and terminal velocity
Drag depends on the speed, shape , roughness and density of the fluid through which it travels
Large cross sectional areas result in a greater drag force
For most objects, drag force is directly proportional to speed^2
Termianl velocity
During vertical fall, weight of the object is constant but drag force increases as speed increases
The instant the object starts to fall, there is no drag force, so resultant forice is weight, and acceleration is g
As the object falls, its speed increases and so drag increases, the resultant force on the object decreases and instantaneous acceleration becomes less than g
Object reaches terminal velocity, where drag force is equal and opposite to its weight
At terminal velocity, object has zero accelation and speed is constant
Centre of mass
centre of gravity - point where the entire weight of an object appears to act
Find centre of gravity
Freely suspended object will come to rest with its centre of gravity vertically below the point of suspension
Insert a pin through the object and llow the object to swing freely
It will come to rest with its centre of gravity vertically below the pin
Hang a plumb line from the pin and draw a line along the vertical string of the plumb-line
Repeat for a different point and the centre of gravity will be the point of intersection of the lines
Centre of mass - point through which an externally applied force produces straight line motion but no rotations