# Y2_T4_LSN_4.1

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ScienceMiddelbare schoolhavo, vwoLeerjaar 2

This lesson contains 25 slides, with interactive quizzes and text slides.

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#### Slide 1 -Slide

Topic 4
Moving in the world

#### Slide 2 -Slide

Plan for today
• Planning topic 4
• Explanation T4.1 Forces
• Make homework

#### Slide 3 -Slide

Planning Topic 4
• Quiz 4.1 - 4.3          in 2 weeks         (counts 2x)
• Test T4 (4.1-4.5)    in test week      (counts 4x)
• Practica                   in 2/3 weeks     (no grade)

4.1 Forces

#### Slide 5 -Slide

Learning goals
I can....
• explain what a force is an can identify different types of forces.
• calculate the gravitational force acting on an object.
• draw arrows on a force diagram with the correct point of application, magnitude, and direction.
• calculate the resultant force of forces going in the same direction or opposite direction of each other
• calculate the resultant force of two perpendicular forces

#### Slide 6 -Slide

Key words
• Force
• Newton
• Gravity
• Applied force
• Muscle force
• Driving force
• Air resistance
• Drag
• Friction
• Tension force
• Spring force
• Elastic force
• Normal force
• Support force
• Weight
• Point of application
• Direction
• Magnitude
• Resultant force

#### Slide 7 -Slide

A world of forces

A force is defined as a push or pull.
• unseen
• see the effects

The unit for forces is in Newtons (N).

#### Slide 8 -Slide

Types of forces

There are different types of forces:
• Gravity = pulls objects towards the earth
• Applied forc = a general force applied to an object (muscle or motor)
• Air resistance  = force between air and an object
• Friction = force exerted by a surface sliding against an object
• Tension force = force spread through a rope or cable when pulled
• Spring force = force when a spring or elastic material is stretched
• Normal force = force supporting an object on a surface

Types of forces

Types of forces
Unit
Also known as
Gravity
Fg
Applied force
Fa
muscle force
driving force
Air resistance
Fair
drag
Friction
Ff
Tension force
Ft
Spring force
Fs
elastic force
Normal force
Fn
support force

Types of forces

#### Slide 11 -Slide

Measuring gravity and weight
The force needed to lift 1 kg = 9.81 N on earth
9.81 is the gravitational constant on earth in N / kg or

On the moon the force needed is only 1.6 N
(So the mass is the same, but the
gravitational force is different)

Weight = the newtons for every kg of an objects mass

9.81 is the gravitational constant on earth in N / kg or

m / s2

#### Slide 12 -Slide

Calculating gravity force
Formula for calculating Gravity force:

Fg is the gravitational force in [N]
m is the mass in [kg]

Fg = m x 9.81

#### Slide 13 -Slide

Calculating gravity force
Example:
The mass of Peter is 70 kg. What is his gravitational force (Fg)?

Fg                        = m x 9.81
Fg  = 70 [kg] x 9.81 [N/kg]
Fg                      = 868 [N]

#### Slide 14 -Slide

Example: The gravitational force of my cat is 34.3N What is her mass ?
Fg

#### Slide 15 -Open question

Example: John has a mass of 76 kg. What is his gravitational force, ?
Fg

#### Slide 16 -Open question

Drawing force diagrams
Forces are represented by an arrow

It has three things:
• Point of application (origin of force)
• Direction
• Magnitude (the longer the arrow, the bigger the force)

For the magnitude you use a scale (in this case 1 cm = 10N)

#### Slide 17 -Slide

A forces is drawn with a length of 4 cm
The scale is 1 cm = 30 N
What is the magnitude of the force drawn?
A
60 N
B
30 N
C
120 N
D
7,5 N

#### Slide 18 -Quiz

I want to draw a force with a magnitude of 300 N.
The scale must be 1 cm = 60 N
How large should the arrow be?
A
2 cm
B
5 cm
C
10 cm
D
12 cm

#### Slide 19 -Quiz

Calculating forces
If there is more than one force acting on an object then the forces can be combined to create one total force = resultant force

Two forces in the same direction are added up
Two forces in opposite direction are subtracted from eachother

If forces are equal and in opposite direction, there is no motion!
Fres

#### Slide 20 -Slide

Calculating forces

#### Slide 21 -Slide

What is the resultant force?
A
140 N to the left
B
140 N to the right
C
60 N to the left
D
60 N to the right

#### Slide 22 -Quiz

What is the resultant force?
A
225 N to the left
B
225 N to the right
C
25 N to the left
D
25 N to the right

#### Slide 23 -Quiz

Perpendicular forces
When two forces are acting perpendicular to each other, you can calculate the resultant force with the abc-formula.

Fres=302+402
=50N
a2+b2=c2

#### Slide 24 -Slide

Homework
• Study the glossary of 4.1
• Complete the exercises of 4.1 (p. 158-161)