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    This module and collection are included inLens: Siyavula: Natural Sciences (Gr. 7-9)
    By: Siyavula

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To build your own dynamometer

Module by: Siyavula Uploaders. E-mail the author

NATURAL SCIENCES

Energy transfers and forces

A. Forces

EDUCATOR SECTION

Memorandum

Groups can assess each other’s dynamometers by determining how effectively they work. Compile a matrix in which the criteria that are to be assessed, as well as the criteria describers, are given. Allow the learners to join you in deciding about this, so that they will know exactly how the dynamometer will be assessed before the start of the project.

The weights of objects of which the weight will be determined will depend on the size of the objects that are used.

Conclusion

The greater the mass of the object, the greater the earth’s gravitational force upon it.

Let us test our knowledge:

(a) A force is exerted on an object, for example by pulling or pushing it.

(b) Newton (N).

(c) Dynamometer/spring-balance.

(d) E.g. 60 kg _______mass; then your weight is ± 600N seeing that 1 kg has the weight of ± 10N.

(e) Weight is the gravitational force of the earth on an object.

(f) Electrostatic force

Gravitational force

Magnetic force

(g) Tensile force

Momentum (thrust)

Rotational force/torque (torsion)

(h) A force can make an object rotate.

A force can halt a moving object.

A force can change the speed of an object.

A force can change the shape of a moving object.

A force can change the direction of a moving object.

(i) c

(j) Rotation

LEANER SECTION

Content

ACTIVITY: To build your own dynamometer [LO 2.4]

Build your own dynamometer

Requirements:

  • Wooden plank (30 mm x 300 mm)
  • Screw (± 25 cm in length)
  • Elastic band
  • Nail
  • Tin can lid
  • String
  • White paper
  • Retort stand and clamp

Step 1: Glue the white paper to the wood.

Step 2: Screw the screw in at the top of the plank.

Step 3: Suspend the elastic band from the screw and clamp the plank in the stand.

Step 4: Use the hammer and nail to pierce four holes at equal distances along the edge of the tin lid.

Step 5: Attach four pieces of string (each ± 150 mm long) to the lid, by tying them through the holes. Tie the four loose ends of string to another length of string (± 300 mm long). Then attach this longer length of string to the elastic band.

Step 6: Make a mark on the paper immediately below the elastic band. This is the O position.

Step 7: Now place the mass pieces (to a total of 102 grams) on the lid. Mark the new position of the elastic band as “1”.

Step 8: Repeat step 7, increasing the mass of the mass pieces as you proceed, until you have marked 5 graduations on the paper. Avoid putting too much strain on the elastic band – if it is stretched too far, it might snap.

You have now built a simple dynamometer calibrated in Newton. 1 N is equal to ± 102 g. One kilogram is therefore equal to approximately 10 N.

Use this dynamometer or another spring balance to determine the weight of the following objects:

Table 1
OBJECT WEIGHT IN N
one pen ______________________N
five such pens ______________________N
your shoe ______________________N
both your shoes ______________________N
an object of your choice ______________________N

Complete:

Deduction:

The greater the___________________________________________, the greater the

______________________________________________. that the earth exerts on it.

4. Let’s see what you know. Do turn back to the earlier work in the module if you are unsure of yourself. This means that you may refer to the module as a source of information.

(a) Write one sentence to explain what we mean when we speak of force.

_____________________________________________________________________

(b) What is the unit that we use for measuring weight? ________________________

(c) Which instrument is used to measure the weight of an object?

_____________________________________________________________________

(d) What is your mass? _________________________________________________

Consider your body as an object. What is the weight of your body in

Newton?______________________________________________________________

(e) What is weight?

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(f) Name three forces that are exerted around us in nature.

______________________________________________________________

______________________________________________________________

______________________________________________________________

_____________________________________________________________________

(g) Name two kinds of force that can be exerted.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(h) Name five effects of forces on objects.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

_____________________________________________________________________

(i) Underline the example that illustrates the force of gravity.

(i) Magnets that repel one another.

(ii) A person doing a long jump.

(iii) A spoon falling off the table and landing on the floor.

(iv) Two people running into one another.

(j) When forces cause an object to move in a circle, we say that they cause

a ________________________________________________________ of the object.

Summative (10)

5. A journey through space

The most difficult part of space travel is escaping the Earth’s gravity. Space travellers need rockets to travel to outer space. A rocket is a powerful engine that is strong enough to overcome gravity and to guide the spacecraft into space.

Figure 1
Figure 1 (graphics1.png)

On 25 April 2002, Mark Shuttleworth became the first South African and African to undertake space travel.

Figure 2
Figure 2 (graphics2.png)

Assessment

Learning Outcome 2:The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

Assessment Standard 2.4: We know this when the learner application of knowledge: applies knowledge appropriately by connecting the learnt concept to a variation of the known situation:

2.4.1: identifies the forms of energy that are transferred.

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