Statics Flashcards
Statics
F(R) = 0N
Object has zero acceleration
Constant Velocity / Stationary
Equilibrium
Statics covers the motion of objects in equilibrium
The net force of an object in equilibrium is zero
Look for ‘constant velocity’, ‘at rest’, ‘no acceleration’
-> Indicates resultant force is 0N
Newtons First Law
An object will continue to move with constant velocity or continue to be at rest unless a resultant force acts on the object
Weight
Distinguish between mass (kg) and weight (N) -> Weight act vertically downwards
W = mg -> g: gravitational field strength pr acceleration of free fall (9.81 ms^-2)
Normal Contact Force / Reaction Force
If an object exerts a force on a surface when the surface exerts an equal and opposite force on the object
This is always perpendicular to the surface
Tension
Acts on a string, cable, rope when pulled tight or compressed
Friction including Air Resistance
Acts in the opposite direction to the motion or velocity of the object
Up thrust
Acts if an object is fully or partially submerged in a fluid
Always acts upwards
Free Body Diagrams
Shows an object with all the forces acting on that object
Forces in the diagram are coplanar
Weight is drawn from the centre of mass
Contact forces are drawn from the point of contact
Closed Vector Triangle
For an object in equilibrium F(R) = 0N, that has three forces acting on it, we can draw the forces as a closed vector triangle
If the triangle is closed, then there is no resultant force
The arrows follow each other
Scale Drawings
Deciding on a scale for the length of the vectors
e.g. 1cm: 100N
Use a protractor to draw angles accurately
We can determine an unknown force by measuring the length of arrow and converting to Newtons using the scale
Scale Drawing Steps
Define Scale
Draw weight to scale
Measure angle
Draw the line at the angle
Measure the other angle and find the intersection -> Intersection shows the length of the forces
Measure T(1) and T(2) in cm
Convert to Newtons
Resolving Vectors to Solve Statics Problems
In equilibrium, the resultant force is zero, meaning the components acting horizontally and vertically add to zero
Horizontal and Vertical Components are Independent of each other
Resolve vectors into horizontal and vertical components
Distinguish between left / right, up / down
Define positive and negative directions
Statics on a Slope
We resolve the vectors into two components - Not Horizontal and Vertical
Split into components parallel and perpendicular to the slope
Typically, there are three forces acting: Weight: W, Friction: F, Normal Contact Force: N
Resolve the weight to parallel and perpendicular components
Parallel: F = WsinΘ -> Parallel Components = 0N
Perpendicular: F = WcosΘ -> Perpendicular Components = 0N
Extra Force to Establish Equilibrium
In some questions, there are two forces acting on an object and causing a resultant force -> Find it, including it’s direction
A third force can be added to make the resultant force = 0N
Equal in magnitude but opposite in direction to the previous resultant force
