3.1 Forces and friction

[lo 1.1; lo 1.3; lo 3.1]

Write a report (three A4 sheets) on Isaac Newton and on his contribution to science. Also refer to the saying 'The apple never falls far from the tree'. Include your report in the module as extra pages following this one.

Assessment of RESEARCH

Were you able to find out who Isaac Newton was and do you understand his contribution to science?

[LO 1.1; LO 1.3; LO 3.1]

Activity:

Describing the relationship between mass, weight and force

[lo 2.3; lo 2.4]

The earth attracts all objects that are in its proximity.

• We know the following:

• all objects have mass and all masses exert tractive force (pull); this mostly is not observable;
• the greater the masses, the greater the tractive force; as the earth is large, we only observe tractive force in one direction (i.e. as the earth attracting our bodies);
• the closer the proximity between masses, the greater the tractive force between them.

• The mass of an object serves as an indication of the amount of matter and this is measured in
• The weight of an object signifies the amount of tractive force (pull) that the earth exerts on the particular object.
• The tractive force which attracts objects to the earth is known as gravitation .
• The unit for measuring force is NEWTON (N).

The weight of an object that has a mass of 100 g is 1 N

• This is roughly equal to the weight of a small banana or a small apple.

Questions:

1. ONE kilogram has a weight of .........................N.

2. Your mass will remain the same, no matter where you may be in the universe, but your weight will vary. Explain this. ( Refer to the module dealing with space programmes.)

3. What is your mass?..................................................

4. What is your weight?..................................................

5. What would your weight be on the moon where the tractive force is 0,6 N?

6. FORCE and WEIGHT are both measured in NEWTON. Explain this.

7. You are able to observe the effect exerted on an object by the force of attraction if you lift it up by means of an elastic band. This demonstrates the principle behind the SPRING BALANCE.

8. Describe the difference between a spring balance and a bathroom scale.

[LO 2.1; LO 2.3; LO 2.4]

Activity:

Measuring force (weight) with a spring balance

[lo 1.2; lo 2.4]

Measure the weight of a number of objects with the help of a calibrated spring balance.

• First measure the weight after suspending the object from the spring balance by means of a length of string.
• Then place the object on the floor and pull it along to get a reading. Note down both readings.
• Repeat each operation three times for each object.

Assessment of the ability to measure weight/force by means of a spring balance

[LO 1.2]

QUESTIONS

1. What is inside the spring balance to make it possible to take a measurement?

2. Why do the two readings differ?

3. What is the meaning of calibrated ?

4. What would the weight of a 2,5-kg bag of sugar be?

5. What is the purpose of the adjustment for zero on the spring balance?

6. Identify the forces that are present.

7. Distinguish between weight and mass.