Forces and newton s 3 laws
Download
1 / 24

Forces and Newton’s 3 Laws - PowerPoint PPT Presentation


  • 62 Views
  • Uploaded on

Forces and Newton’s 3 Laws. What is a force?. Push or pull Produce changes in motion or direction. Net force:. The net force is a combined total force acting on an object. F net ΣF

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Forces and Newton’s 3 Laws' - trisha


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

What is a force
What is a force?

  • Push or pull

  • Produce changes in motion or direction


Net force
Net force:

  • The net force is a combined total force acting on an object.

  • Fnet

  • ΣF

  • We represent force by using vectors- arrow symbols that represent magnitude and direction by their length and which way they point.


Let s look at forces acting on this box
Let’s look at forces acting on this box:

FN – The Normal Force- table pushing up on

the box- THIS IS ALWAYS PERPENDICULAR

TO THE SURFACE AND EQUAL TO THE Fg.

Stationary:

F1 = -20 N west

F2 = 20 N east

10 kg

Fg

What is the Fnet acting on this box:

ΣF = Fnet = -20 N + 20 N = 0

FORCES ARE BALANCED

A Fnet of zero means no change in movement.

The box stays stationary.


Let’s look at forces acting on this box:

FN

Stationary:

F1 = 20 N west

F2 = 40 N east

10 kg

Fg

What is the Fnet acting on this box:

ΣF = Fnet = -20 N + 40 N = 20 N east

FORCES ARE UNBALANCED

Now the Fnet is not zero which means there is a change

in movement. This box is not going to remain stationary.


Let’s look at forces acting on this box:

FN

Stationary:

F1 = 20 N west

F2 = 40 N east

10 kg

Fg

What is the Fnet acting on this box:

ΣF = Fnet = 20 N + 40 N = 60 N east

FORCES ARE UNBALANCED

Again there is a non-zero Fnet which means there is a change

in movement.


But what if the box had an initial motion
But what if the box had an initial motion:

FN

Moving with a constant velocity:

F1 = -20 N west

10 kg

F2 = 20 N east

Fg

What is the Fnet acting on this box:

ΣF = Fnet = -20 N + 20 N = 0

FORCES ARE BALANCED

The Fnet is zero which means there is not a change

in movement or direction. This box is continues to move

with a constant velocity.



What about when the box is already moving with a constant velocity
What about when the box is already moving with a constant velocity?

What would cause the box to stop?

10 kg

UNBALANCED FORCES

What would happen if there weren’t unbalanced forces? Would the box ever stop?…


Not according to newton s 1 st law of motion
…Not according to velocity?Newton’s 1st Law of Motion:

An object at rest has a natural tendency to stay at rest, or an object in motion will stay in motion, unless a force is acting upon it.

This is also known as the law of INERTIA.

INERTIA is an objects resistance to change in motion.


Examples of inertia
Examples of INERTIA: velocity?

1. Not wearing your seatbelt- if you get into an

accident your body wants to keep moving at

the speed you were going.


2 the famous tablecloth trick
2. The famous tablecloth trick: velocity?

http://www.youtube.com/watch?v=D-a3kwvY0WM


The relationship between mass and inertia
The relationship between mass and inertia: velocity?

MASS IS A MEASURE OF INERTIA- the more massive the object, the more that object tends to resist changes in its state of motion.

What would be easier to push a small car or a semi?


Adding mass into the mix brings us to newton s 2 nd law of motion
Adding mass into the mix brings us to velocity?Newton’s 2nd Law of Motion:

If I push both vehicles with the same amount of force

which one would accelerate more? Why?

Which turns into Newton’s 2nd equation:


m/s velocity?2

kg

kg • m/s2 = Newton = N


A medium sized apple weighs about one newton
A medium-sized velocity?apple weighs about one Newton.


Let s find the magnitude of the acceleration for this box if the following forces are applied
Let’s find the magnitude of the acceleration for this box if the following forces are applied:

FN

F1 = -20 N

F2 = 40 N

10 kg

Fg

a = ?

Fnet = ΣF = -20 N + 40 N = 20 N

m = 10 kg

=


This leads us to the f g
This leads us to the F if the following forces are applied:g:

g = 9.81 m/s2 ~ 10 m/s2

What’s mass times the acceleration due to gravity?

THIS IS WEIGHT


Use the weight equation to find your mass
Use the weight equation to find your mass: if the following forces are applied:

This needs to be in N. Use 1 N = .22 lbs


Let s go back and talk about our box again this time analyzing all the forces
Let’s go back and talk about our box again this time analyzing all the forces:

FN – EQUAL but OPPOSITE to the Fg = 100 N

F1 = -20 N

F2 = 20 N

10 kg

-100 N

Fg = ma = mg =

Now we are dealing with forces acting in two directions (x and y).

ΣFy = Fnety = 100 N + -100N = 0

ΣFx = Fnetx = -20 N + -20N = 0

This box is not moving or changing

direction.


Practice with newton s 2 nd
Practice with Newton’s 2 analyzing all the forces:nd:

1. A tractor pulls a loaded wagon with a constant force of 400 N. If the total mass of the wagon is 200 kg, what is the wagon’s acceleration?


2. A broken down car is being pushed to the side of the road with a force of 200 N which is causing it to accelerate at .2 m/s2. What is the mass of the car?


3. The car below was moving with an initial velocity of 50 m/s until F2 was applied to slow the car down. What is the deceleration of the box?

F1 = 300 N

F2 = -500 N

10 kg

What is the distance the box travels before it comes to a stop?



ad