TTO2 - unit 2

• Science
• Middelbare school
• vwo
• Leerjaar 2

Goals of Today

1. Explain the difference between weight and mass?

2. Explain what elastic means?

3. Explain what extention means?

4. Explain Hooke's Law for springs.

5. Work in pairs: theoretical & practical knowledge.

Assignment

Grab all your belongings (bag, books, pens).

The people who did the practical with the springs last week stand at the back of the class room.

The people who did NOT do the practical stand at the front.

Now within a minute find a partner and sit down.

Ready to start.

Unit 2.1 Mass & Weight

Do I weigh the same on the moon and on the earth?

1. yes
2. no
3. idk (I don't know)
4. you can't tell

Explain why on the moon and on the earth you weigh the same.

But why is it that on the moon you can't keep your feet on the ground?

Mass and weight

Both on earth and on the moon you have the same mass.

Same amount of atoms/molecules, so same amount of matter.

On earth the gravitational field strength / gravity 
is larger than on the moon.

So you weight on earth is larger than on the moon.

Mass m in kilogram (kg)

Gravitational Force F_g in Newton (N)

Weight

Measure with Newtonmeter.

"Calculate" from mass.

1 kg = 10 N

Formula: F_g = m . g (g = 9,81 N/kg or 10 N/kg same as acceleration of free fall)

Unit 2.2 Density

Why does this happen?

Density
What do you remember about this topic?
Use key words

Definition:
The density of a substance is the mass of a unit of volume of it.

The density of a substance depends on two things:

1. the mass of the atoms (particles)

2. how closely the particles are packed together 

What can the unit of density be?

Density

Definition: 
The density of a substance

is

The mass of a unit of volume of it.

Unit: 

​cm​3​​​​g​​=g.cm​−3​​

<-- SI unit

​m​3​​​​kg​​=kg.m​−3​​

What is the formula for density?

Density

Definition: 
The density of a substance

is

The mass of a unit of volume of it.

Unit: 

Formula: 

​m​​kg​​​3​​=kg​​​​​m​−3​​

​cm​3​​​​g​​=g.cm​−3​​

ρ=​V​​m​​

Calculation

In your notebook:

Using the calculation procedure
calculate the density of a log of oak wood which has a volume of 2000 cubic centimeter and a mass of 1,8 kg.

Calculation

1. Draw a cuboid (NL: balk).
Label the sides length l, width w, height h
Give the formula for the volume V.

2. Draw a cylinder.

Label the diameter d and the height h.

Give the formula for the volume V.

Copper has a greater density than water, so the coin sinks.
Wood has a smaller density than water and so the log floats.

Unit 2.3 Force & shape

A ball is elastic.
What does "elastic" mean in this sentence?

Test

Rubber bands

An object is said to be elastic
if it regains its original shape
when the forces that deform it
are removed.
Which words need explanation in this sentence?

The extension of a spring is 2 cm.
What does "extension" mean
in this sentence?

Do this at home

Goals of Today

1. Explain the difference between weight and mass?

2. Explain what elastic means?

3. Explain what extention means?

4. Explain Hooke's Law for springs.

Extension

The extension of a spring / strip of material
at any stage
= its length at that stage - its initial length

Calculate the extension of the springs

in this illustration.

Hooke's Law for springs

The extension of a spring

is directly proportional to

the weight it supports.

Formula:

F = k . x 

F = force

x = extension

k = spring constant (different for each spring)

Explain what this means to each other in pairs

In practice how can you see that Hooke's Law applies to the springs
you used?

1. The extension u increases with more force F
2. Spring 1 increases less than spring 2
3. The extension of spring 1 and 2 together always adds up to the same total
4. F/u shows more or less the same number for each column.

What is the quantity k in Hooke's Law called?

When plotting the graph of F against u,
what shape should the graph have?

Which line has the largest spring constant k?

blue, red, green

Goals of Today

1. Explain the difference between weight and mass?

2. Explain what elastic means?

3. Explain what extention means?

4. Explain Hooke's Law for springs.

Unit 2.4 and 2.5

Write down words/concepts you need help with from unit 2.4 and 2.5

Write one sentence about what you learnt this lesson.

What do you need next lesson, last lesson before the test?