Flashcards in Mechanics Deck (109)
What is a vector quantity?
A physical quantity with magnitude and direction.
What is a scalar quantity?
A physical quantity with only magnitude.
Give three examples of scalar quantities.
Give five examples of vector quantities.
When can vector quantities be added together?
When the vectors are parallel or antiparallel.
How can resultant vectors be calculated?
How are vectors added using a scaled diagram?
-The vectors are drawn to scale and joined head to tail in the correct direction.
-The resultant vector joins the polygon.
What are the components of a vector?
The perpendicular pair of vectors.
How can vectors be added by resolving components?
-The vertical and horizontal components of the vectors are calculated.
-The perpendicular components are added and the resultant vector calculated.
What is the component parallel to the slope of a weight?
What is the component perpendicular to the slope of a weight?
Which forces acting on a weight are parallel to the slope?
Which forces acting on a weight are perpendicular to the slope?
-Normal reaction force
What is a moment?
A force that produces a turning effect given by force x perpendicular distance from the line of action of the force to the pivot.
What is a moment also known as?
How can a moment be increased?
What is the principle of moments?
At balance, the sum of the clockwise moments about a point is equal to the sum of the clockwise moments about the same point.
What is the centre of gravity?
The point from which all the weight of an object appears to from.
Explain how the centre of gravity of a lamina can be found.
-Make a small hole in the corner of the shape and suspend it from a pin so it can move freely.
-Hang a plumb line from the pin and mark the vertical line.
-Repeat for two more points.
-The point of intersection shows the centre of gravity.
How can an object be made stable?
-Low centre of mass.
-Large base area.
When will an object tip over?
When the centre of gravity passes outside the base.
What is statics?
The study of forces acting on stationary objects.
What is Newtonian mechanics?
The study of objects that obey Newton's three laws of motion.
Define coplanar forces.
Forces that all act in the same plane.
What happens when the vectors acting on a point form a closed polygon?
There is no resultant vector.
Give the two conditions for static equilibrium of coplanar forces.
-The resultant vector must be zero.
-The principle of moments must apply.
What is the principle of concurrency?
For three coplanar forces in equilibrium, the lines action must all pass though one point. (be concurrent)
What does the principle of concurrency apply to?
An object acted on by three forces.
The study of forces that may result in motion.