Lecture 2 - Recorded on September 10, 1999
1-Dimensional Kinematics, Speed, Velocity, Acceleration
Video Lectures: (RM-80K) (RM-300K)
This lecture is an introduction to kinematics which ultimately leads (in Lecture 4) to trajectories in 3 dimensions.
Lectures.
| SEG # |
SEGMENT TITLES |
SEGMENT TOPICS |
STARTS AT (MIN:SEC) |
| 1 |
Introduction to 1-Dimensional Motion |
Professor Lewin describes 1D motion of a particle. He talks about average velocity, the importance of "+" and "-" signs, and our free choice of origin. |
00:00 |
| 2 |
Average Speed vs. Average Velocity |
The two are VERY different. The average velocity can be ZERO, while the average speed is LARGE. |
05:19 |
| 3 |
Instantaneous Velocity |
Considering the incremental change in position x with time t, we arrive at v=dx/dt. The instantaneous velocity is the derivative of the position with respect to time. Professor Lewin reviews when the velocity is zero, positive and negative; he distinguishes speed from velocity. |
06:56 |
| 4 |
Measuring the Average Speed of a Bullet |
Professor Lewin shoots a bullet through two wires. The average speed can be calculated from the distance between the wires and the elapsed time. All uncertainties in the measurements are discussed; they have to be taken into account in the final answer. |
11:05 |
| 5 |
Introducing Average Acceleration |
The average acceleration between time t1 and t2 is the vectorial change in velocity divided by (t2-t1). |
17:35 |
| 6 |
Instantaneous Acceleration |
The acceleration, dv/dt, is the derivative of the velocity with time. It is the second derivative of the position x with time. Professor Lewin shows how to find the sign of the acceleration from the slope in an x-t plot. |
24:46 |
| 7 |
Quadratic Equation of Position in Time |
When the position is proportional to the square of the time, the velocity depends linearly on time, and the acceleration is constant. |
27:24 |
| 8 |
1D Motion with Constant Acceleration |
Professor Lewin writes down a general quadratic equation for the position as a function of time, and he relates the constants in this equation to the initial conditions at time t=0. The gravitational acceleration is a constant (9.80 m/s^2 in Boston), and it is independent of the mass and shape of a free-falling object, if air drag can be ignored (see Lecture #12). You can use this result to measure g using the free fall time measurements from the falling apples in lecture 1. |
34:18 |
| 9 |
Strobing an Object in Free Fall |
Professor Lewin drops an apple from 3.20 m and takes a polaroid picture of the falling apple which is illuminated by a strobe light. First two light flashes per second, and then ten flashes per second. |
41:17 |