Forces - air resistance, friction, weight Flashcards
In the absence of air resistance, only the falling object’s ______ acts on it. How is this calculated?
weight; multiply m (object mass) by g (Earth’s gravitational force, 9.81 ms^-2)
Value of “g” on Earth
9.81 m/s
When does a falling body reach terminal velocity? What occurs?
When its weight is balanced by air resistance, causing resultant force to be zero. At terminal velocity the object ceases acceleration, maintaining a constant speed.
Free fall
The motion of a body where the only force acting on it is gravity.
Name the two forces acting upon a falling body, and state whether they are upward or downward.
Air resistance; upward
Weight; downward
Cause of air resistance
Collision of falling body with air particles in Earth’s atmosphere generating an upward force.
Uniform/non-uniform acceleration examples + definition
Def + e.g. – uniform: acceleration remains constant, does not increase or decrease. Occurs when an object is in free fall
Def + e.g – non-uniform: acceleration increases or decreases over time. Happens to a falling body experiencing air resistance
As speed increases, air resistance:
a) decreases
b) remains constant
c) increases
c)
A heavier object encounters _____ air resistance than a lighter one.
a) more
b) less
a)
Elastic vs plastic behaviour
Elastic behaviour: The material returns to its original size and shape after having the forces deforming it removed
Plastic behaviour: The material retains its deformation it takes after having the causal forces removed.
Hooke’s Law
Force applied and the extension of an elastic object (elastic deformation) are directly proportional prior to reaching the limit of proportionality.
Friction
A force always acting in the opposite direction to motion, slowing objects down and preventing them from sliding over one another
Cause of friction
The coarseness of sliding surfaces, sometimes at a microscopic scale
Effects of friction
Heat generation, damage to/erosion of mobile surfaces
