Chap 4: Dynamics II - Forces Flashcards
What is Newton’s first law of motion?
every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it
Another name for Newton’s first law?
law of inertia
What is a balanced force?
When all the forces acting on an object is balanced and the resultant force is zero
What happens to an object when its resultant force is zero? (balanced force)
object can be…
- at rest
- or in constant velocity
the acceleration is ZERO
Define inertia
reluctance of an object to change its state of rest or motion due to mass
Does mass affect inertia?
Yes
The greater the mass, the more inertia
What is Newton’s Second Law of Motion?
when a resultant force acts on an object of constant mass, object will accelerate in direction of resultant force
When are forced unbalanced?
when the resultant force is NOT zero, so there will be acceleration
How to calculate resultant force?
product of mass and acceleration
F=ma
What are the effects on a resultant force?
causes objects to:
- move
- stop
- change velocity
Effects on Newton’s second law of motion?
objects can be accelerating or decelerating
What is Newton’s third law of motion?
for every action, there’s an equal and opposite reaction
four key points of newton’s third law
- forces occur in pairs (action & reaction)
- action and reaction are equal in magnitude
- action and reaction act in opposite directions
- action and reaction act on different bodies
2 main points to consider when drawing free body diagrams
- include ONLY object of interest
- and all external forces acting ON the object itself
How to find resultant force?
vector addition or drawing vector diagram
What happens when 3 forces balance each other? (equilibrium)
- resultant force is zero
- forms a closed triangle
Define friction
a contact force that opposes or tends to oppose motion between surfaces in contact
Examples of positive effects of friction?
- walk without slipping with friction
- objects can slow down if needed with friction
Examples of negative effects of friction?
- cars are less efficient
- causes wear and tear
How to reduce negative effects of friction?
use:
- wheels
- ball bearings
- lubricants and polished surfaces
- air cushion
How to enhance positive effects of friction?
use:
- treads
- parachutes
- chalk
What happens when objects fall without air resistance? [gravity only]
- objects experience free fall
- constant acceleration of 10m/s^2
- free fall on dependant on mass or size
What happens to objects that falls with air resistance?
object falls with decreasing acceleration
How to reduce air resistance?
have a streamlined shape
Define terminal velocity
when air resistance equals weight
- object travels at constant speed
- zero acceleration, constant velocity
What does air resistance do?
- opposes motion of object
- increases with speed of object
- increases with size/surface area of object
- increases with density of air
