**1. What is mass and what is weight?
2. Give examples of where there is potential energy and
where there is kinetic energy?
3. What affects the potential energy and the kinetic energy?
4. What is an inclined plane and what can it be used for
considering the above question?
5. Solve simple calculations about work and energy
6. Questions**

**What is
mass and what is weight?**

*Mass:*

The mass is the substance of an object, i.e. how many kilos
or grams the object contains. The mass of an object does not
change if it moves out into space. The substance of the
object is the same.

*Weight:*

The weight of an object depends on the attractive force
towards the center of the Earth. Or, if placed on another
planet â€“ the attraction force towards the center of that
planet. This attractive force is called gravity.

On Earth the gravitational force is 10 N for each kilo of
the object. An object with a mass of one kilogram has the
weight 10 N. Similarly; an object with the mass 2 kg has a
weight of 20 N.

If however the object is moved to the Sun, the object will
have a bigger weight. This is because the Sun has a greater
attractive force on the object. This makes an object with
the mass 1 kilo having the weight 274 N.

The moon is smaller thus having a lesser attractive force on
the object. An object with a mass 1 kilo has a weight of
1.62 N on the moon.

The gravitational force on a planet has to do two things.
First, it depends on the planet's mass and secondly, the
distance of the object to the planet center. The greater the
planet mass is, the greater the gravitational force
(attractive force). Further, the closer the object is to the
planet center, the greater the gravitational force
(attractive force).

Consider an astronaut jumping ahead on the moon. Each jump
takes the astronaut higher above the lunar surface compared
to if doing the same jump on the Earth's surface.

Weight = Mass (kg) * g-force acceleration (10 m/s^{2}
on earth)

G = weight (N)

m = mass (kg)

g = g-force acceleration (10 m/s^{2} on earth)

Eg. The weight of a kilogram on Earth: G = m * g = 1 kg *
10 m/s^{2} = 10 N

**Give examples of where there is
potential energy and where
there is kinetic energy?**

*Figure 1: Potential energy converted to kinetic energy*

Look at the picture above. A stone is lifted 10 meters above
the earthâ€™s surface. The stone has a certain amount of
potential energy. This is because the stone can later on
drop towards the ground. If the stone falls its potential
energy is released.

When the stone is falling towards the ground, the stoneâ€™s
potential energy is converting gradually into kinetic
energy.

At any time during the fall, we can freeze the fall so that
the stone is hanging in the air. If we analyze the
situation, we can see that the distance the stone has fallen
has been converted into kinetic energy. The distance the
stone has left to fall can also be converted into kinetic
energy, but until then, the remaining energy is potential
energy.

Remember that no energy is lost - it can only be converted.
On impact all kinetic energy is converted into frictional
heat.

**What affects the potential energy and the
kinetic energy?**

*Potential Energy:*

If an object can fall in a gravitational field, the object
has potential energy. Potential energy is relative, meaning
that if we lift a spoon and place it on a table, we can say
that the spoon has a certain potential energy compared to
the floor. If an elevator shaft is right next door, we can
say that the spoon has a greater potential energy towards
the ground floor of the building. How much energy it is,
depends on how long the object can fall, or how high it is
lifted.

If the object has a great mass, this will also increase the
potential energy as the object is lifted.

*Kinetic Energy:*

When an object having a certain speed, we say that the
object has a certain kinetic energy. The object may be a car
traveling on a highway or spoon falling to the ground.

**What is an inclined plane and what can it be used for
considering the above question?**

*Figure 2: An inclined plane*

The ball is at a certain height (h). The ball has a certain
mass (m). The height is given in meters and the mass in
kilograms. The inclined plane is on the earth where the
g-force acceleration (g) is 10 m/s^{2}.

If the ball is released and rolling down the inclined plane
the potential energy is gradually more and more converted
into kinetic energy. When the ball has rolled all the way
down to the ground floor all the potential energy is
converted into kinetic energy.

**Solve simple calculations about
work and energy**

*Potential Energy:*

How big the potential energy is depends on the objectâ€™s mass
(m), g-force acceleration (g) and how high it is located.

The formula to calculate the potential energy:

W = energy (unit: Joule (J))

m = mass (unit: kilograms (kg))

g = g-force acceleration (10 m/s^{2} on earth)

h = height (unit: meter (m))

Eg.

A stone of 10 kg is lifted 10 m up in the air. What is the
stone's potential energy?

m = 10 kg

g = 10 m/s^{2}

h = 10 m

W = ?

==> Wp = m * g * h = 10 kg * 10 m/s^{2} * 10 m = 1000 J

Answer: __The rock's potential energy is 1000 J__

*Mechanical Work*

Mechanical work is done when a constant force is used making
an object move a certain distance. If an object is dragged
on the ground a friction needs to be continuously overcome.
There is required a force to move the object. Mechanical
Work is done.

Formula for Mechanical Work:

W = energy (unit: joule (J) or Newton meters (Nm))

F = force (unit: Newton (N))

d = distance (unit: meter (m))

*Figure 3: The mechanical work in this example is 2000 Nm.
A frictional force of 200 N is overcome.*

W = F * d = 200 N * 10 m = 2000 Nm

1. On which planet would you get the best high jump results - on the Moon or Jupiter?

2. Which of the following planets has the greatest gravitational pull (attractive force) - "Jupiter or Saturn" â€“ why â€“ look in a collection of tables and look for planet gravitations?

3. Explain to a friend what mass is?

4. Explain to a friend what weight is?

5. What is the difference between mass and weight?

6. What is the unit of force?

7. What is the unit of weight?

8. What is the unit of mass?

9. What is g-force acceleration?

10. What is the g-force acceleration on earth and the moon?

11. How do you calculate the weight if you have the mass of an object?

12. What is the weight of each respective mass on earth?

1 kg = N

2 kg = N

200 grams = N

2 t = N

0.5 kg = N

3 hg = N

13. Tell us about your potential energy when you are in school?

14. How do you calculate the potential energy?

15. What determines how big the potential energy is?

16. What is kinetic energy?

17. Describe how potential energy can become kinetic energy?

18. Describe the role of an inclined plane when it comes to describing potential energy and kinetic energy?

19. An object is raised 3 m up in the air. The object has a mass of 3 kg. How big is the potential energy?

20. An object is lifted 5 m up in the air. The object has a mass of 300 kg. How big is the potential energy?

21. An object is lifted 100 m up to the air. The object has a mass of 0.5 kg. How big is the potential energy?

22. An object is raised 3 m up in the air. The object has a weight of 3 N. What is the potential energy?

23. An object is lifted 100 m up in the air. The object has a weight of 1 N. What is the potential energy?

24. An object is dragged 20 m on the ground with the force 50 N. How much mechanical work is done?

25. Felix Mashed potatoes contain 1450 kJ per 100 grams dry matter. How much mashed potatoes do you need to eat in order to drag an object 20 m with the force 20 N? (Then of course, it is needed energy to carry the body load and so on during the trip, but we will not take that into account here).

26. How far can you drag the object in the above question, if you eat 100 grams Felix mashed potatoes?

By Dr. Sandor A. Markus

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