(Drawing) Forces

• Natuurkunde
• Middelbare school
• vmbo lwoo
• Leerjaar 2,3

The normal force

The normal force is a passive force which is a reaction to the force applied on a surface.

Look at the examples below. The boxes do not fall through the floor and the man cannot push through a tree since in reaction to the gravitational force on the box and the muscle force of the man the ground and the tree push back. This "push" back force is called the normal force.

Drawing forces

A force is a vector. This vector has a magnitude, direction and point of application. 

Every force has a name and unit.

The symbol for a force is: F

The symbol for its unit is: N (Newton).

When drawing forces you make use of a force scale which is explained in the next slide.

Force scale

To be able to draw a force you need to agree upon the relation between the size of the force and the length of the vector you are drawing. 

We call this agreement the force scale.

Example 1:

A force of 20 N using a force scale of 5 to 1 is drawn as 4 centimeter long vector.

Example 2:

A vector with a length of 12 centimeter, using a forcescale of 5 to 1 resembles a force with a size of 60 Newtons.

Example 3:

A force with a size of 60 Newton and with a vector length of  4 centimeter has used a force scale of 15 to 1 (1 cm ≘ 15 N).

Resultant force 1

When multiple forces are at work om an object in the same horizontal or vertical plane, then you may add or substract these forces.

substract

add

But if multiple forces are 

at an angle with each other, you need to use the parallelogram method or head to tail method.

Resultant force 2

If forces are at work on an object at an angle with each other you use the head to tail or parallelogram method.

Head to tail; simple add up the forces by adding them head to tail. Where you finally end up is where the resultant force is pointing to.

Parallelogram: this method looks a lot like as if you have used the head to tail method two times in a row. The final result of both F1 and F2 is called the resultant force Fr

Find the resultent F(r) of the rubber boat, and sent a picture of your drawing.

0

What is the magnitude F(res) of the skier

Fill in the answers like:
p: ...N etc.

"the ball moves more slowly at the end"

what force does play a major role in this?

1. gravitational force kleefkracht
2. muscle force
3. friction
4. tension

What will happen?

if two forces even each other out?

1. an object's speed will decelerate
2. an object's speed will accelerate
3. The resultant force will increase
4. an object will rest or move with a constant speed

Geef van alle drie de onderdelen van de brug aan of hier trekkrachten, duwkrachten of allebei plaatsvinden.

Pilar

Cable

Road surface

Tension

Compression

Both

Choose the
one which does
not apply here

1. Gravitational force
2. Tension
3. Electric force
4. Muscle force

Choose the odd one out

1. Tension
2. Centrifugal force
3. Friction
4. Gravitational force

Choose the odd one out

1. Magnetic force
2. Airfriction
3. Electric force
4. Gravitational force

When will the resultant force
at maximum size?

1. when forces are directed opposite to each other
2. when forces are directed in the same direction
3. when forces are at a large angle with each other
4. when forces are perpendicular to each other

Calculate and draw
the resultant force

What will be the force scale?

1. 1 cm = 5 Newton
2. 2 cm = 50 Newton
3. 1 cm = 100 Newton
4. 1 cm = 10 Newton

Copy this drawing and mark the resultant force as well

The car drives at a constant speed.

Calculate the airfriction

1. 1000 N
2. 1500 N
3. 2000 N
4. 2500N

The weight of a scooter is 1569,6 N.
What will be the mass?

1. 160 kg
2. 180 kg
3. 200 kg
4. 220 kg

On the moon the gravitational force will be 6 times smaller than on earth. When your mass is 48 kg, what will then be your mass on the moon?

1. 48 kg
2. 8 kg
3. 5 kg
4. 42 kg

What force do you need to pull up a mass of 1 kilogram?

1. 9,81 N
2. 981 N
3. 10 N
4. 100 N

A force can do three things.

tell me what they are

When drawing forces three things are important

tell me what they are

A cup stands on your table.

What can you tell me about the resultant force in this situation?

Copy this drawing and mark the resultant force as well

A cup (m=500g) rests on your table.

calculate the normal force (g=9,8 m/s²)