Unit 2 - Forces Flashcards
What 2 effects will a force have on a body?
Change its position in space
Deformation (to some degree - ignored in rigid body mechanics)
What is the difference between mass & weight?
Mass = quantity of matter in a body
Weight = force of gravity on a body (m x g)
How do you calculate density?
p = mass/vol
What does the amount of friction between two surfaces depend on?
Roughness, magnitude of force pushing them together, lubrication
Independent of surface area
How to calculate friction force?
F = µN
µ = coefficient of friction (measure of maximum friction force) N = force acting normally to surface
What are the 3 difference types of friction?
Static - exists only when motion is about to occur (once max friction force exceeded motion will being)
Sliding - exists only when sliding occurs between surfaces (sliding friction less than static)
Rolling - arises due to deformation of 2 surfaces by force acting normally when rolling (less than sliding friction)
Define pressure
F/A
when force acts perpendicularly to surface
What is meant by static equilibrium?
No resultant force (therefore at rest of constant velocity)
Sum of external forces = 0
Newton’s 3rd law?
To every action there is an equal and opposite reaction
Newton’s 1st law (of inertia)
Every body remains at rest or at a constant velocity unless acted upon by a resultant force
Inertia - tendency to do nothing or to remain unchanged (a body’s inertia is represented by its mass)
Newton’s 2nd law (of acceleration)
F = ma
Related to dynamic equilibrium when the sum of the external forces does not = 0
Equation for momentum?
p = mv
What is the principle of conversation of momentum?
The total momentum of a system is constant if there are no external forces acting
Equation for moments?
M = Fd
How do you calculate mechanical advantage?
MA = Effort arm/resistance arm
Why do muscles mostly work at mechanical disadvantage?
The closer a muscle inserts into a joint then the smaller the change in muscle length required to produce a correspondingly larger limb movement
Quicker movement
Describe the 3 classes of lever
1st - fulcrum between effort & resistance (can be adv/dis)
2nd - resistance between fulcrum & effort (always adv)
3rd - effort between fulcrum & resistance (always dis)
What is the relationship between linear & angular velocity?
v = rω
Linear velocity acts at a tangent
What is the equation for tangential acceleration?
a(t) = rα
Represents the linear acceleration directed at a tangent to the circle (equal to 0 during uniform angular motion)
What is the equation for centripetal (radial) acceleration?
a(r) = v^2/r = rω^2
Acts towards centre of rotation to maintain body in circular path
What is the moment of inertia?
Sum of the products of the mass of each particle of the body and the square of its perpendicular distance from the axis of rotation
dependent on how the body’s mass is distributed
Equation for moment of inertia?
I (moment of inertia) = mk^2
(k = radius of gyration)
Rotary version of F=ma:
t = Iα
t = torque (force)
What is meant by radius of gyration?
When considering rotary motion it is useful to consider the mass of a body being concentrated at a certain radius (of gyration) from the axis
What is the equation of angular momentum?
L = Iω
Equation for work?
w = Fd
Equation for power?
P = w/t
Equation for kinetic energy?
KE = 1/2mv^2
1/2Iω^2 for rotary motion
Equation for potential energy?
PE = mgh
Principle of conservation of energy?
Energy can never be created or destroyed, only changed from one form to another
