# Plane Curvilinear Motion - Indian Institute of Technology ... Notes/ME101-Lecture23-KD.pdf ...

date post

30-Jun-2018Category

## Documents

view

223download

0

Embed Size (px)

### Transcript of Plane Curvilinear Motion - Indian Institute of Technology ... Notes/ME101-Lecture23-KD.pdf ...

Kinematics of Particles

Plane Curvilinear MotionMotion of a particle along a curved path which lies in a single plane.

For a short time during take-off and landing,

planes generally follow plane curvilinear motion

1ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles

Plane Curvilinear Motion:

Between A and A:

Average velocity of the particle : vav = r/ t

A vector whose direction is that of r and whose

magnitude is magnitude of r/ t

Average speed of the particle = s/ t

Instantaneous velocity of the particle is defined as

the limiting value of the average velocity as the time

interval approaches zero

v is always a vector tangent to the path

Extending the definition of derivative of a scalar to include vector quantity:

Magnitude of v is equal to speed (scalar)

2

Derivative of a vector is a vector having a magnitude and a direction.

ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles

Plane Curvilinear MotionMagnitude of the derivative:

Magnitude of the velocity or the speed

Derivative of the magnitude:

Rate at which the length of the position vector is changing

Velocity of the particle at A tangent vector v

Velocity of the particle at A tangent vector v

v v = v

v Depends on both the change in magnitude of v and

on the change in direction of v.

3

vsdtd vrr /

rdtdrdtd //r

ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles

Plane Curvilinear MotionBetween A and A:

Average acceleration of the particle : aav = v/ t

A vector whose direction is that of v and whose

magnitude is the magnitude of v/ t

Instantaneous accln of the particle is defined as

the limiting value of the average accln as the time

interval approaches zero

By definition of the derivative:

In general, direction of the acceleration of a particle

in curvilinear motion neither tangent to the path

nor normal to the path.

Acceleration component normal to the path points

toward the center of curvature of the path.

4ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles

Plane Curvilinear MotionVisualization of motion: Hodograph

Acceleration has the same relation to velocity as the velocity has to the position

vector.

5ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles

Plane Curvilinear MotionDerivatives and Integration of Vectors:

same rules as for scalars

V is a function of x, y, and z, and an element of volume is

Integral of V over the volume is equal to the vector sum of the three integrals of its

components.

6ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles

Plane Curvilinear Motion

Three coordinate systems are commonly used for describing the vector

relationships (for plane curvilinear motion of a particle):

1. Rectangular Coordinates x-y

2. Normal and tangential coordinates n-t

3. Polar coordinates r- (special case of 3-D motion in which cylindrical

coordinates r, , z are used)

Choice of coordinate systems depends on

the manner in which the motion is generated

or the form in which the data is specified.

7ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles: Plane Curvilinear MotionRectangular Coordinates (x-y)If all motion components are directly expressible

in terms of horizontal and vertical coordinates

8

Also, dy/dx = tan = vy /vx

Time derivatives of the unit

vectors are zero because their

magnitude and direction remains

constant.

ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles: Plane Curvilinear MotionRectangular Coordinates (x-y)

Projectile Motion An important applicationAssumptions: neglecting aerodynamic drag, Neglecting curvature and rotation of

the earth, and altitude change is small enough such that g can be considered to

be constant Rectangular coordinates are useful for the trajectory analysis

For the axes shown in the figure, the acceleration components are: ax = 0, ay = - g

Integrating these eqns for the condition of constant accln (slide 11) will give us

equations necessary to solve the problem.

9ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles: Plane Curvilinear MotionRectangular Coordinates (x-y)

Projectile Motion

Horizontal Motion: ax = 0

Integrating this eqn for constant accln condition

Vertical Motion: ay = - g

Integrating this eqn for constant accln condition

10

Subscript zero denotes

initial conditions: x0 = y0 = 0

For the conditions under

discussion:

x- and y- motions are

independent

Path is parabolic

xx

x

xx

vvxxavv

tvxxattvxx

vvatvv

00

2

0

2

00

2

00

00

2

2

1

+

02

0

2

0

2

0

2

2

00

2

00

00

22

2

1

2

1

yygvvyyavv

gttvyyattvyy

gtvvatvv

yy

y

yy

+

ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles: Plane Curvilinear MotionNormal and Tangential Coordinates (n-t)Common descriptions of curvilinear motion uses Path Variables: measurements

made along the tangent and normal to the path of the particle.

Positive n direction: towards the center

of curvature of the path

Velocity and Acceleration

en = unit vector in the n-direction at point A

et = unit vector in the t-direction at point A

During differential increment of time dt, the particle

moves a differential distance ds from A to A.

= radius of curvature of the path at A

ds = d

Magnitude of the velocity: v = ds/dt = d/dt

In vector form

Differentiating:

Unit vector et has non-zero derivative because its direction changes.

11ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles: Plane Curvilinear MotionNormal and Tangential Coordinates (n-t)Determination of t:

change in et during motion from A to A

The unit vector changes to etThe vector difference det is shown in the bottom figure.

In the limit det has magnitude equal to length of

the arc et d = d

Direction of det is given by en

We can write: det = en d

Dividing by dt: det /dt = en (d/dt) en

Substituting this and v = d/dt = in equation for acceleration:

Here:

12

22

22

tn

t

n

aaa

sva

vv

a

ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles: Plane Curvilinear MotionNormal and Tangential Coordinates (n-t)Important Equations

In n-t coordinate system, there is no component

of velocity in the normal direction because of constant for any

section of curve (normal velocity would be rate of change of ).

Normal component of the acceleration an is always directed towards the center of the

curvature sometimes referred as centripetal acceleration.

If the particle moves with constant speed,

at = 0, and a = an = v2/

an represents the time rate of change in the dirn of vel.

Tangential component at will be in the +ve t-dirn

of motion if the speed v is increasing, and in the

- ve t-direction if the speed is decreasing.

If the particle moves in a straight line, =

an = 0, and a =

at represents the time rate of change in

the magnitude of velocity.

Directions of tangential components

of acceleration are shown in the figure.13

v

22

22

tn

t

n

aaa

sva

vv

a

ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles: Plane Curvilinear MotionNormal and Tangential Coordinates (n-t)

Circular Motion: Important special case of plane curvilinear motion Radius of curvature becomes constant (radius r of the circle).

Angle is replaced by the angle measured from any radial reference to OP

Velocity and acceleration components for

the circular motion of the particle:

14

circular motion general motion

22

22

tn

t

n

aaa

sva

vv

a

v

ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles: Plane Curvilinear MotionRectangular Coordinates (x-y)Example

The curvilinear motion of a particle is defined by vx = 50 16t and y = 100 4t2.

At t = 0, x = 0. vx is in m/s2, x and y are in m, and t is in s. Plot the path of the

particle and determine its velocity and acceleration at y = 0.

Solution:

Calculate x and y for various t values and plot

15ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles: Plane Curvilinear MotionRectangular Coordinates (x-y)Example

Solution:

When y = 0 0 = 100 4t2 t = 5 s

16ME101 - Division III Kaustubh Dasgupta

Kinematics of Particles: Plane Curvilinear MotionRectangular Coordinates (x-y)Example: The rider jumps off the slope at 300 from a height of 1 m, and remained

in air for 1.5 s. Neglect the size of the bike and of the rider. Determine:

(a) the speed at which he was travelling off the slope,

(b) the horizontal distance he travelled before striking the ground, and

(c) the maximum height h

Recommended

*View more*