Science Form 1: 1.5 Weight and mass

What is Weight?

1 Earth's gravity pulls all objects to its centre.
2 The weight of an object is a result of the force of gravity.
3 The weight of an object is not constant. It changes from one place to another, depending on the force of gravity acting on the object.
4 The weight of an object is greater at the poles than at the equator. This is because the force of gravity is greater at the poles.
5 The weight of an object can be measured using a spring balance. The length of the spring with an object is directly proportional to the force acting on it.
6 The SI unit for measuring weight is newton (N).



Spring Balance
7 The unit newton or kilogram-force is normally used in scientific investigations. One newton is almost equal to one tenth of a kilogram-force.
8 The compression balance can also be used to measure weight.
9 Before measuring an object, you must check that the spring indicator is at the zero mark.

What is Mass?
1 Mass is the quantity of matter contained in an object.
2 The mass of an object does not change because the quantity of matter contained in it is the same wherever the object is.
3 The lever balance or the beam balance is used to measure the mass of an object.



4 The lever balance is easier to use because the mass of the object can be read directly. With a beam balance, the mass of the object needs to be balanced with a standard mass. There are two scales on a lever balance. The first scale measures from 0 g to 250 g. The second scale measures from 0 g to 1 000 g.
5 The SI unit for mass is the kilogram (kg).

The Difference between Mass and Weight

1 Weight and mass are two different quantities.
2 The weight of an object depends on the Earth's gravitational pull. The greater the gravitational force, the greater the weight of the object.
3 The mass of an object is the amount of matter that it contains.

The Menstrual Cycle

1 The menstrual cycle marks the sexual maturity of a girl.

2 A girl is born with all the eggs that she will release throughout her life.

3 For fertilisation to take places a mature ovum must be released from one of the female's ovaries.
4 About once every 28 days, a mature ovum is released into the Fallopian tube during a process called ovulation.

5 (a) If the ovum is not fertilised, menstruation takes place.
(b) Menstruation is the breakdown of the uterus lining and its gradual discharge through the vagina.
(c) Menstruation lasts from four to five days.
(d) The length of a menstrual cycle is the number of days from the first day of one menstruation to the first day of the next menstruation.

6 (a) The menstrual cycle is the monthly cycle of changes that occur in the walls of the uterus, the ovary and the vagina,
(b) The walls of the uterus undergo changes that are closely related to the development and release of the ovum.



7 A complete menstrual cycle involves
(a)Menstruation
(b) changes in the thickness of the walls of the uterus
(c) the development of the ovum in the ovary
(d) ovulation (the release of the ovum)

8 Figure shows the thickening of the uterine lining and the changes that occur in the ovary throughout the menstrual cycle.

Menstruation
•24 hours after ovulation, the unfertilised ovum dies.
•The thick lining of the uterus is not needed and starts to break down.
•The unfertilised ovum together with the uterine lining and blood are shed and menstrual flow begins.
•Menstruation stops after about three to five days.