Topic 3.1 : Forces

• Science
• Middelbare school
• havo
• Leerjaar 2

Topic 3.1 : Forces

Learning goals:

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

Topic 3.1 : Forces

Forces are all around us, You can’t see them !

You can only see their effect

Object changes shape

Object starts to move

Object changes speed

Direction of object changes

Topic 3.1 : Forces

Object changes shape

Topic 3.1 : Forces

Object starts to move

Topic 3.1 : Forces

Object changes speed

Topic 3.1 : Forces

Object changes direction

Topic 3.1: Forces

There are many types of forces

Types of forces	Unit	Also known as
Gravity	F g
Applied force	F a	muscle force
Air resistance	F air	drag
Friction	F f
Tension force	F t
Spring force	F s	elastic force
Normal force	F n	support force

Topic 3.1: 
Forces

Air resistance force

Gravity force

Spring force

magnetic force

Normal Force

Tension Force

applied force

Friction force

Topic 3.1: Forces

Force (F)

Measured in Newtons (N)

The force needed to lift 1 kg = 9.8 N on earth

On the moon the force needed is only 1.6 N

The mass is the same

Gravitational force is different

Topic 3.1: Forces

Formula for calculating Gravity force

F_g is the gravitational force in [N]

m is the mass in [kg]

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

F_g = m x 9.8

m / s²

Topic 3.1: Forces

Example: 

The mass of Peter is 76 kg. What is his gravitational force, F_g?

F_g                        = m x 9.8 

F_g = 76 [kg] x 9.8 [N/kg]

F_g                      = 744.8 [N]

The mass of Mohamed is 45 kg. What is his gravitational force, Fg

1. 350 N
2. 45 N
3. 441 N
4. 882 N

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

1. 34,3 kg
2. 3,5 kg
3. 336 kg
4. 24,5 kg

Topic 3.1 : Forces

Forces are represented by an arrow

It has three things:

1. point of application (origin of force)

2. direction

3. magnitude (the longer the arrow, the bigger the force)

Topic 3.1: Forces

1. point of origin: 

Centre of mass

2. Direction: 

downward

3. Magnitude:

depending on scale

Name types of forces

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?

1. 60 N
2. 30 N
3. 120 N
4. 7,5 N

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 (vector) be?

1. 2 cm
2. 5 cm
3. 10 cm
4. 12 cm

Topic 3.1: Forces

Adding up forces (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!

What is the resultant force?

1. 140 N to the left
2. 140 N to the right
3. 60 N to the left
4. 60 N to the right

What is the resultant force?

1. 225 N to the left
2. 225 N to the right
3. 25 N to the left
4. 25 N to the right

Topic 3.1: Forces

Adding up forces that are not in one line

Head-tail method

begin to end = resultant force

Forces can't be seen.
What effects of a force can be seen?

1. changes in shape
2. changes in temperature
3. changes is color
4. changes in density

A person on earth has a mass of 80 kg. What is the gravitational force?
Only give your answer and unit

Topic 3.1 : Forces

Learning goals:

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