Chapter 5: Dynamics Flashcards
Distinguish between mass and weight
Mass = amt. of matter in an object; measure of inertia; fixed
Weight = gravitational force exerted on a mass (by Earth)
What is inertia?
Resistance to changes in motion
mass is a measure of inertia
state the relation between mass and weight (formula)
W = m x g
when there is no gravity, weight will be 0
more mass means more inertia means more weight
How to draw free body diagram
x represents the object
balanced forces must be the same length
length of lines must be the same for a stationary object
length of lines = force magnitude
What is normal contact force? (NCF)
Force that holds the object up, usually perpendicular to where object is in contact with ground
Describe the tension arrow thingy for more than one point (because tension arrows have like 3 things)
Two types of tension = upper tension and lower tension
upper tension is the horizontal tension, the 2 upper tensions should cancel each other out
Each diagonal arrow has a vertical component
vertical component of both sides added up = weight
length of arrows must reflect this (i.e length of arrows should add up to the total length of W)
What is Newton’s first law?
An object will remain in its state of rest or motion in a straight line with constant speed unless acted upon by a non-zero net force (resultant force)
What is Newton’s second law
The rate of change of momentum is proportional to the resultant force and takes place in the direction of the force
Formula for force, F
F = m x a
inertial mass = F/a
a = F/m
F and a act in the same direction; a is proportional to F; a is inversely proportional to m
What happens to the motion of a particle once force is applied?
Depending on the initial motion of the particle:
1) Stationary –> start moving (to the right)
2) Moving to the right –> speed up
3) Travelling to the left –> slow down
4) Travelling (slowly) to the left –> stop moving
5) Change in direction (no change in speed)
Heavier objects need more force to accelerate
A student has a mass of 50 kg and is able to accelerate vertically upwards by 8.0 m s-2 to make a leap (this happens when she is in contact with the ground)
By applying Newton’s law, explain how she achieved her acceleration
The ground exerts and upwards force greater than her own weight
according to Newton’s 2nd law, the difference between these forces produces a resultant force
she accelerates with a magnitude that is proportional to the resultant and in the direction of the resultant
