class presentation outline for projectile motion created for cvca physics by dick heckathorn 28...

Class Presentation Outline for

Projectile Motion

Created for CVCA PhysicsBy

Dick Heckathorn28 November 2K+4

Needs updating from short one

Table of Contents

3 A projectile is4 Dropping an object5 Laser Disk A: 41, 42, 43, 447 Dropping an Object9 Throwing Horizontally

11 Dropping a Super Ball12 Laser Disk B: 11, 12, 13, 14, 1522 Problem: Thrown Horizontal24 Problem: Horizontal Up28 Problem: Horizontal Down p 205 # 4531 Assumptions

A projectile is:

Any object that moves through the air or through space acted only on by gravity (and air resistance if any).

We will ignore air resistance unless information relative to it is stated.

Dropping an object.

The only force acting on the object is the pull of the earth acting on it in a down direction.

This causes the object to accelerate at the rate of 9.8 m/s2 in the same downward direction.

A 41 Free Fall Ride

Falling on Demon Drop

Accelerometer Shown

Always parallel to tracks

A 42, 43 Falling Bowling Ball

Bowling ball released from 4 m

A 44 Falling “Down Under” in Australia

Object dropped in both

New York and Australia

Droping an object

To analyze the motion one uses the five kinematic equations with the variables: a, vi , vf , d and t.

Remember that you can use one of the calculator programs to find any two variables given the other three.

Coffee Filter Investigation

Handout: #13 Air Resistance

Motion Sensor on Ceiling

Computer

Lab Pro

TI-83+

Printer – Online & Epson FX

Throwing an Object Horizontal

If one assumes that there is no gravitational force of the earth on the object…

it will travel in a horizontal direction with a constant velocity.

Relative variables are: vh, dh, and t.


It we deal with reality, there is the force of gravity acting on the object.

How does this force affect the horizontal component of the motion of the object?


Demo: Super Ball

We can see that the force of gravity acting on the ball does not affect the horizontal motion which is at right angles to the direction of the force of gravity.

B 11 Projectile Motion

Ball was projected horizontally, another dropped straight down

Later, horizontally lines drawn

Old PSSC – large white balls


Ball shot horizontally from crossbow as a target ball is dropped horizontally. Both originally aligned horizontal.



Ball shot at an upward angle from crossbow as a target ball is dropped horizontally.



Ping pong balls glued to plexiglas sheet at equal time intervals

Old PSSC – Professor Hume

B 15a Projectile Motion

Air table is tilted so pucks respond to “diluted gravity”.

One shot horizontal, one dropped.

Frame 3573

B 15b Projectile Motion

Frame 3914

Determine range of angle

vs

angle of shot.

B 15c Projectile Motion

Frame 4385

Shot-putter


We have seen that:

the horizontal and vertical components do not affect each other

the vertical motion is that of free fall.


Each component can be analyzed independent of each other.

We do so according to the following:


Horizontaldh

vh

t

Verticalavi

vf

dv

t

Problem 1An object is thrown horizontally at 27 m/s from the edge of a cliff which is 40 m above the ground.

a. How long does it take to reach the ground?

b. What is the range of the ball? (Horizontal distance)

c. With what velocity did it strike the ground?

Solve for ‘t’ by: ?The velocity as it strikes the ground: ?The value for vf is: ?Solve for dh : ?

Horizontal

dh =

vh =

t =

Verticala =vi =vf =dv = t =

How long to reach the ground?We are given and know:

27 m/s

40 m ↓

9.8 m/s2 ↓0 m/s

2.86 s

28 m/s ↓2.86 s

77.2 m

38.9 m/sH 46.0o D

Problem 2

An object is thrown with a speed of 725 m/s at an angle of H 60o U.

a. How long does it take to reach the ground?

b. What is the range of the ball? (Horizontal distance)

c. With what velocity did it strike the ground?

First find the horizontal and vertical component of the initial velocity.

60o

730 m/s

365 m/s

632 m/s

632 m/s ↓

We are given and know:

The value for dv is: ?Solve for dh is: ?The velocity as it strikes the ground: ?Solve for t by: ?

Horizontal

dh =

vh =

t =


365 m/s

20379 m ↑

9.8 m/s2 ↓632 m/s ↑

64.5 s

0 m/s129 s

47085 m

730 m/sH 60.0o D

64.5 s nono

632 m/s ↓

OR

The value for dv is: ?Solve for dh is: ?The velocity as it strikes the ground: ?Solve for t by: ?

Horizontal

dh =

vh =

t =


365 m/s

20379 m ↑

9.8 m/s2 ↓632 m/s ↑

129 s

129 s

47085 m

730 m/sH 60.0o D

Problem 3

A bomber, diving at an angle of 53o with the vertical, releases a bomb at an altitude of 730 m. The bomb hits the ground 5.0 sec after being released.

Problem 3

53o

202 m/s

First find the horizontal and vertical component velocities of the bomb.

161.2 m/s

121.5 m/s

The value for vf is: ?The value for t is: ?

We are given and know:

The value for dh is: ?

Horizontal

dh =

vh =

t =


730 m ↓

9.8 m/s2 ↓121.5 m/s ↓

5.0 s

170.5 m/s↓161.2 m/s

5.0 s

806 m

The velocity as it strikes the ground: ?

___ m/sH ____ D

Assumptions Projectile Motion

1. The effect air resistance has been ignored.

Air resistance will shorten the horizontal distance a ball will go.

A baseball projected to go120-m will only go 71.4-m.


2. The acceleration due to gravity is constant.

We will find that the acceleration due to gravity varies inversely proportional to the square of the distance from the center of the earth.


3. The earth is assumed to be flat as the circumference is very large.

Thus for large horizontal distances the calculated distance is not exactly correct.


4. Projectile remains in same vertical plane during flight.

A projectile launched directly north will not follow the longitudinal line from which it is launched due to the rotation of the earth on its axis.

Need for a computer

When sending a rocket to the moon, constant calculations are needed to update the corrections need to get the rocket to the moon.

When the computers went down on Apollo 13, there was nothing to update the data.

Apollo 13 Video

Scene when aligning up spacecraft to enter earth’s atmosphere at the correct angle.

Article

Notes from the Military

That’s all folks!

class presentation outline for projectile motion created for cvca physics by dick heckathorn 28...

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