# 9: Review of Lectures 1 through 5

{'English - US': '/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/lecture-9/lec9.srt'}

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Topics covered: This lecture reviews selected topics previously covered in lectures 1 through 5.

Instructor/speaker: Prof. Walter Lewin

Date recorded: September 27, 1999

## Video Index

Please make sure you play the Video before clicking the links below.

• Scaling Arguments
The cross-sectional area of femurs should scale with mass if mother nature were protecting the femurs of large animals from crushing. But that is not the case. The diameter of a femur scales with its length. That protects the femurs against buckling (sideways deformation).

• Dot Products
Two methods are reviewed for obtaining the scalar product, by decomposition and by projection.

• Cross Products
The magnitude of the cross product equals the product of the magnitude of the two vectors and the sine of the angle between them. The direction of the vector product is determined using the right-hand corkscrew rule.

• 1D Kinematics
A graphic example of the position x(t) is given, and the velocity and acceleration are derived at various points in time. The average velocity and average speed are calculated. A plot of velocity vs. time is constructed.

• Trajectories
Trajectories lie in a plane; they therefore reduce to 2 dimensional problems. A detailed example is worked using the trajectory of the "zero gravity" experiments in the KC135 (see Lecture 7).

• Uniform Circular Motion
The parameters for uniform (constant speed) circular motion are reviewed, including the equations for angular velocity and centripetal acceleration. The numerical example worked out is NASA's centrifuge to test astronauts; the centripetal acceleration is about 10g!

• Brain Teaser with a Yardstick
Professor Lewin slides his fingers underneath a yardstick, towards the center. Something strange happens, the fingers seem to take turns moving, they alternate sliding and stopping. Can you explain this?