Unit 1 - FORCES Handout

 

Forces - any straight-line ______________   or ______________

 

A.    Representing Forces

 

1.      Unit of force

 

a)    lb. (English)

 

b)    ______________ (metric) (weight of one ___________) ****

 

 

2.      Forces are vectors - described using ___________   & ___________

 

 

Solving problems with vectors require a special branch of mathematics

 

   Review - Scalar (   ______________   only) ex) ______________

 

 

3.      When solving problems and drawing pictures, forces are represented as

 

_______________

 

                                   

                                                                                   

                                                    

                                   

                                   

                                                                                                                                    

           

           

***Length shows ____________***arrow shows _____________

B.      Combining Force Vectors

 

Resultant­ ________________________________

 

 

            1)         Methods for finding resultant.

 

(a) Case 1     -   ___________________

 

       (Angle between forces = ______________)

 

                       

 

Answer:

 

 

            RULE when Р  =  0 _________________________

 

           

 

 

 

(b)  Case II    - Forces acting in _______________

 

                                              

 

 

 

 

 

 

Resultant = _________________

 

 

 

 

 

RULE

If Р = 180° - __________ _________________________________________________

 

 

 

 

 

 

 

 

 

 

 

 

(c) Case III   Forces acting at an angle

 

C.    Combining Forces - Range of possible resultants

 

 

Example) Forces of  100N and 30N force act on a body. 

 

 

¨      Largest possible resultant =  ______________

 

¨      Smallest possible resultant = ______________

 

 

ü      ______________ Forces - Smallest Possible Resultant

 

ü      ______________ Forces - Largest Possible Resultant

 

 

 

 

 

Example - Which pair of concurrent forces may have a resultant of 20nt?

 

 

¨      Big Hint: Find the range of possible resultants for each choice (nt = Newtons)

 

 

a)    5 nt     + 10 nt                                    

b)    20 nt  +  20 nt                                 

c)     20 nt  +  50 nt                                 

d)    30 nt  +   5 nt                                  

 

Answer _______________

 

 

D.     Finding resultants when angle between forces = 90°

 

Ex 1)   A 5N force pulls an object north while a 12 N force is pulling the object West. Find the resultant

Scale 1N = 1cm     

                                                                                               

 

 

 

 

 

 

 

 

 

 

Two Methods

 

Method One - Graphical Method -(Draw It!!)

 

1.      _______________________________________________

 

2.      _______________________________________________

 

3.      _______________________________________________

 

4.      _______________________________________________

 

 

 

 

 

 

 

 

 

 

 

 

 


Method Two - Use trig. and Pythagorean (More accurate and easier)

 

 

1.      Use a2 + b2 = c 2 (To find magnitude)  _______________

 

 

2.      Tanq =  Opp./Adj =                       q = _________

 

 

 

 

 

 

E.      Equilibrant  - the balancing force of 2 or more vectors

 

The Equilibrant is always_______________________________________

 

___________________________________________________________________________

 

 

ü      If…                  Resultant  = 5 N 53°  N of W

 

ü      Then…           Equilibrant  = __________________

 

 

 

 Example 2) Concurrent forces (acting together) of 10 nt east and 10 nt south act on an object. 

Find the resultant and the equilibrant.

  

 

1.      ____________________

                                                                                     

2.      __________________

 

 

Answer:  Resultant = __________________ Equilibrant  = ____________