# 1-6 Drawing forces

Lesson goals:
• Draw or sketch a force diagram when forces work in different directions.
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Slide 1: Slide
NatuurkundeMiddelbare schoolvwoLeerjaar 3

This lesson contains 22 slides, with interactive quiz and text slides.

Lesson duration is: 50 min

## Items in this lesson

Lesson goals:
• Draw or sketch a force diagram when forces work in different directions.

#### Slide 1 -Slide

Vector
A vector has magnitude,
direction and a point of application.

We draw a vector with an arrow:
• The length of the arrow indicates the size of the force.
• The direction of the arrow indicates the direction of the force.
• The place where the arrow begint indicated the point of application of the force.

#### Slide 2 -Slide

Equilibrium
When two equal forces act in opposite directions. For example, a book that lies on a table.
Normal
When forces are in equilibrium we say the resultant force
equals 0N
(Fr)

#### Slide 3 -Slide

Resultant force
The sum of all te forces.
Also called: nett force or sum force.
(Fr)

#### Slide 4 -Slide

Forces acting in the same direction...

#### Slide 5 -Slide

Forces acting in opposite direction...
are subtracted.

#### Slide 6 -Slide

do the exercises 13 to 21

#### Slide 7 -Slide

Combining forces
• Sometimes you have forces acting
in different diractions.
• In this case you get the resultant
force by combining the forces.
• Both the size and magnitude of the resultant force is important in your answer.

#### Slide 8 -Slide

Steps for drawing a vector diagram
Step 1 - Choose a scale
(e.g. 1 cm = 5N, so 15 N = 3 cm)
Step2 – Think about the point of application and the direction.
Stap 3 – Draw the force
Example: Draw a force of 60N to the right.
Scale 1cm = 10 N

#### Slide 9 -Slide

Parallelogram method
1. Choose an appropriate scale.
2. Draw the forces on scale using the given angle (like two adjacent sides of a parallelogram).
3. Complete the parallelogram.
4. Draw an arrow from the starting point to the opposite corner of the parallelogram.
5. Measure the length of the arrow, give magnitude and direction.

#### Slide 10 -Slide

Example from the book (p. 17)

#### Slide 11 -Slide

Do exercise 22 (p. 19)
timer
6:00

#### Slide 13 -Slide

Do exercise 23 (p. 19)
timer
3:30

#### Slide 15 -Slide

Do exercise 24 (p. 19)
timer
3:30

#### Slide 17 -Slide

Perpendicular forces
When two forces are acting perpendicular to each other, you can calculate the resultant force with pythagoras.
Fres=302+402
=50N

#### Slide 18 -Slide

Perpendicular forces
You can then calcualtet he angle of the resultant force using
tan(α)=F2F1

#### Slide 19 -Slide

Homework
Test yourself 1.2

#### Slide 20 -Slide

What did you
learn today?

#### Slide 21 -Mind map

Conclusion:
When forces act in different directions
you have to combine the forces.
You can use the parallelogram method.
When the forces at at an angle of 90 degrees then you can calculate the unknown side using pythagors.