Ch.3 Linear Motion in 1 D

LINEAR MOTION in 1 DPhysics Grade X

SMA IBC 2015-2016Devilim, S.Si.

Devi, Physics SMA IBC, 2015-2016

Subtopic:• Definition, difference, and examples: Distance, displacement, speed, velocity, acceleration, relative velocity• Linear motion with constant velocity GLB• Linear motion with changing velocity constant acceleration GLBB

• Free-fall object• Graph of linear motion


What is…• Distance• Displacement• Speed• Velocity• AccelerationWhich one belongs to vector?Relative velocity?


Relative Velocity

• Being seen by person C, What is velocity of : A, B, D?• Being seen by person B, what is velocity of : A, C, D?• Being seen by person A, what is velocity of : B, C, D?• Being seen by person D, what is velocity of : A, B, C?


Relative velocity (more of it)

• According to A, what is velocity of: B, C?• According to B, what is velocity of: A, C?• According to C, what is velocity of: A, B?



Linear Motion with Constant VelocityVelocity does not change

Speed :


Conceptual Question:can velocity be negative?


Exercise:A turtle and a rabbit engage in a footrace over a distance of 4.00 km. The rabbit runs 0.500 km and then stops for a 90.0-min nap. Upon awakening, he remembers the race and runs twice as fast. Finishing the course in a total time of 1.75 h, the rabbit wins the race. (a) Calculate the average speed of the rabbit. (b)What was his average speed before he stopped for a nap?




Runner A is initially 4.0 km west of a flagpole and is running with a constant velocity of 6.0 km/h due east. Runner B is initially 3.0 km east of the flagpole and is running with a constant velocity of 5.0 km/h due west.a. How far are the runners from the flagpole when they meet?b. If both of the runners started to run at the same time, when will they meet?



Linear Motion with Constant AccelerationVelocity changed accelerationAcceleration :


If acceleration is constant, then its average velocity:

From combination of those two equations, we can get:


3 equations for Constant Acceleration:





Special Case: Free-fall Object• Object falls down moves vertically towards earth

• Accelerated acceleration = ?• How to find its velocity?• If we throw stone upward, what is the maximum height it can travel to?

• How much time passed until the stone fall down to earth?Assumption in free-fall object:

- No air resistanceDevi, Physics SMA IBC, 2015-2016

3 equations for Constant Acceleration:

For free-fall, change :acceleration to gravity



Example:



Graphs of Linear MotionGraphs have y and x line

> displacement (y) vs. time (x)> velocity (y) vs. time (x)> acceleration (y) vs. time (x)

Graphs of linear motion with constant velocityGraphs of linear motion with constant acceleration



Gradient of :Displacement-time velocity-time


Area of :Velocity-time Acceleration-time


Example:Object moves with constant acceleration:

Graph of:Displacement-time velocity-time acceleration-time



Exercise:Consider a rubber ball dropped from some position above the ground A onto a hard surface B. The ball bounces up and down several times.Figure below shows displacement–time graph for 4 bounces.


Question:


Figure below gives the acceleration a(t) of a Chihuahua as it chases a German shepherd along an axis. In which of the time periods indicated does the Chihuahua move at constant speed?




Exercise:



The velocity vs. time graph for an object moving along a straight path is shown in Figure P2.22. (a) Find the average acceleration of the object during the time intervals 0 to 5.0 s, 5.0 s to 15 s, and 0 to 20 s. (b) Find the instantaneous acceleration at 2.0 s, 10 s, and 18 s.


How far does the runner whose velocity–time graph is shown in Fig. 2-37 travel in 16 s? The figure’s vertical scaling is set by vs = 8.0 m/s.



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Ch.3 Linear Motion in 1 D