Physics 103 Lecture 3 Position & Velocity with constant 物理103讲3位&；速度常数.ppt

Physics 103 Lecture 3 Position & Velocity with constant 物理103讲3位&amp；速度常数
*
Medical Physics, Winter 2019/14, Vit019/14, Vita-Salute San Raffaele University
*
Use of Kinematic Equations
Shows velocity as a function of acceleration and time
Use when you don’t know or need the displacement
Gives displacement as a function of velocity and time
Use when you don’t know or need the acceleration
Gives displacement given time, velocity & acceleration
Use when you don’t know or need the final velocity
Gives velocity as a function of acceleration and displacement
Use when you don’t know or need the time
Example for motion with a=const in 1D: Free fall
*
Medical Physics, Winter 2019/14, Vita-Salute San Raffaele University
*
The Guinea and Feather tube
Earth’s gravity accelerates
objects equally, regardless
of their mass.
Experimental observations:
*
Medical Physics, Winter 2019/14, Vita-Salute San Raffaele University
*
Example 2
A ball is thrown vertically upward. At the very top of its trajectory, which of the following statements is true:
1. velocity is zero and acceleration is zero2. velocity is not zero and acceleration is zero3. velocity is zero and acceleration is not zero4. velocity is not zero and acceleration is not zero
correct
Acceleration is the change in velocity. Just because the velocity is zero does not mean that it is not changing.
At the top of the path, the velocity of the ball is zero, but the acceleration is not zero. The velocity at the top is changing, and the acceleration is the rate at which velocity changes.
Acceleration is not zero since it is due to gravity
and is always a downward-pointing vector.
*
Medical Physics, Winter 2019/14, Vita-Salute San Raffaele University
*
Dennis and Carmen are standing on the edge of a cliff. Dennis throws a basketball vertically upward, and at the same time Carmen throws a basketball vertically downward with the same initial speed. You are standing below the cliff observing thi