October 20, 1998
Let's first review kinematics then look at the posted sample test then at keys to the test.
TWO BASIC CONCEPTS
V = DX/Dt and a = DV/Dt
X = Position Along the Path of Motion.
V = Velocity Along the Path of Motion.
a = Acceleration
apath changes magnitude of V.... slope of graph of v vs t.
aperp changes direction of V.... aperp = V^2 / R
Ways to picture motion.
Motion diagrams.... dots along the path
Graphs... position - time..... velocity - time
Samples and how to think
Motion Diagram... Constant acceleration pattern
Velocity pattern... 0, V, 2V, 3V, 4V, etc.... a = DV/Dt
Position pattern .........Intervals X, 3X, 5X, 7X
Total X, 4X, 9X, 16X
Putting same information in a Graph
Velocity Time Graph... slope: a = DV/Dt
Area: DX = V Dt
Position Time Graph... slope: V = DX/Dt
Analyzing motion with vectors of Velocity, Acceleration
Interactive Physics samples of motion... apath, aperp, v
Orbits, Projectiles, Roads, Hills, Pendulum
Sample Test Questions
Discussion of Test
Changing from Kinematics to Dynamics... introduce mass, m, of object that is moving with velocity, V, and has acceleration, a.
Interactive Physics... the Pendulum.
Multiplying V and a vectors by mass m
m V is called "motion" or momentum
m a is called "net force"... F = ma
Newton stated that the net external force on a body causes acceleration of the body
a = DV/Dt
m a = D(mV)/Dt
F = m a = D(mV)/Dt
Interactive Physics with Pendulum... adding Ftotal.
But what are real forces.
Non-contact forces.... Gravity F = G M m/r^2 = m g
Contact force... String
Add Gravity and String forces to Pendulum
So where did Ftotal come from... diagonal of parallelogram.
Other types of forces.
Interactive Physics ... block on surface.