3 Constructing Hypotheses

ISPS : CONSTRUCTING HYPOTHESES

KPLI & KDPM LECTURE NOTES

MR. SYLVESTER SAIMON SIMIN, MPKS2

INTRODUCTORY INFORMATION

• A hypothesis is a statement of your best prediction as to the relationship between two variables, the MANIPULATED VARIABLE and the RESPONDING VARIABLE.

• A hypotheis should be TESTABLE ie. It should point the way towards the DESIGN of an experiment to test it.

• Expressed as an “IF…….THEN……” sentence. This form, while not always necessary, is a useful way to learn to write a hypothesis.


STEPS FOR WRITING HYPOTHESIS

1. Identify variables in a given event or relationship.

2. Identify a pair of variables that might be logically related.

3. Identify the manipulated and responding variables.

4. Write the hypothesis using the format:• If the (MV) increases / decreases, then the

(RV) will increase / decrease


EXAMPLE 1PROBLEM / QUESTION

Rosli raises bees. He noticed that different numbers of young hatched from the same number of hives at different times. He wondered what factors might influence the hatching rate of bees. He selected the following variables to be tested:

1. Temperature of the hive2. Relative humidity inside the hive3. Amount of food available4. Number of bees living in the hive.

Construct a hypothesis for each variable listed above.


ANSWER FOR EXAMPLE 11. As the temperature of hive increases, the

hatching rate will increase.

2. As the relative humidity inside the hive increases, the hatching rate will decrease.

3. As the amount of food available decreases, the hatching rate increases.

4. As the number of bees living in the hive increases, the hatching rate decreases.


EXAMPLE 2PROBLEM / QUESTION

What factors determine the rate at which an object falls through air?

List 4 possible variables and construct a hypothesis for each variable.


ANSWER FOR EXAMPLE 2Possible variables:a. Volume of objectb. Surface area of objectc. Length of falld. Weight of objectHypothesis:Volume of object

As the volume of an object increases, the rate at which it falls through air decreases.

Surface area of objectAs the surface area of an object increases, the rate at which it falls through air decreases.

Length of fallThe longer or farther an object falls through air, the faster it will fall

Weight of objectThe more weight and object has, the faster it will fall through air


IT’S YOUR TURN (EXERCISE 1)

PROBLEM / QUESTION

Why is it warmer in one house than another?



SAMPLE ANSWER – EXERCISE 1

• Outside temperature– The higher the outside temperature, the higher the temperature

inside the house.

• Location of house– The nearer the house is to the equator, the higher the

temperature inside the house.

• Slope of roof– The steeper the roof, the higher the temperature inside the

house.

• Thickness of insulation– The thicker the insulation, the higher the temperature inside the

house.

• Number of openings to the outside– The more openings (windows and doors) to the outside, the

lower the temperature inside the house.



PROBLEM / QUESTION

What factors determine the length of a shadow?




• Height of object– The taller the object, the longer its shadow.

• Time of day– The closer the time moves toward noon, the

shorter the shadow of an object.

• Season of year– As the season progresses from summer to

winter, the length of a shadow becomes longer.



PROBLEM / QUESTION

What factors determine the number of fleas on two types of dog, a golden retriever and a dachshund?




• Size of dog– If dogs are larger, then they will have a larger

flea population than smaller dogs.

• Length of hair– If dogs have longer hair, then they will have

more fleas than dogs with shorter hair.

• Presence of flea collar– If dogs have flea collars, then they will have

fewer fleas than dogs without flea collars.


EXERCISE 4Which of the following are stated as hypotheses?1. As more salt is dissolved in water, the water will

become cloudy.2. The earth’s crust contains 90 elements.3. Magnetism and gravity are not the same.4. If the length of a vibrating string is increased,

the sound will become louder.

1, 4Remember, a hypothesis is stated as the predicted effect one variable (MV) will have on another (RV)


EXERCISE 6Which of these statements are hypotheses?

1. As the temperature of its environment increases, the temperature of a cold-blooded animal increases.

2. Glass is harder than iron; therefore glass will scratch anything which is softer than iron.

3. A change in weather causes a change in mood

1, 2, 3In all three cases we are predicting what will happen to a responding variable if we manipulate another variable.


EXERCISE 7Which of these statements are hypotheses?

1. If clouds act as insulators, then the earth should get colder on cloudless nights.

2. Leaves manufacture food, stems transfer food, and roots store the food in plants.

3. The colder the temperature, the slower plants grow.

4. The deeper one dives, the greater the pressure.

5. Algae are living organisms.

1, 3, 4


EXERCISE 8Read the description of investigations in the

following slides. Then, answer the following questions.

1. What are some of the constants?

2. What variable was manipulated?

3. Which variable was expected to respond?

4. What was the hypothesis being tested?


EXERCISE 8 – INVESTIGATION 1

John was interested in determining the effect the number of plants located in an area has on growth rate. He planted radish seeds in several milk cartons. In the first carton, he planted 5 seeds 1 cm deep and no less than 5 cm apart; in the second, 10 seeds were planted 1 cm deep and no more than 2 cm apart; in the third, 15 seeds, 1 cm deep and 1 cm apart; and in the fourth, 20 seed, 1 cm deep and 0.5 cm apart. Each carton was watered daily and daily measurements of the length of leaves were made.


ANSWER FOR EXERCISE 8 – INVESTIGATION 1

1. Factors that were kept the same:• Kind of seed, planting depth, type of soil,

environmental temperature, amount of water, kind of containers, and amount of light received.

2. Manipulated variable : number of plants in an area

3. Responding variable : Growth rate (OD = length of leaves)

4. As the number of plants in an area increases, the length of the leaves will become shorter. OR As the number of plants in an area increases, the length of the leaves will become longer


EXERCISE 8 – EXPERIMENT 2Is there a relationship between the amount of training received and the length of time a learned behaviour persists in insects? Select a number of sowbugs which always turn right when entering the intersection of a T-shaped maze. Using the tendency of sowbugs to avoid light, it is possible to train them to turn left by shining a strong-light from the right as they enter the intersection. Subject an animal to 1, 5, 10, 15, or 20 training sessions. Test each animal once an hour by running it through the T-maze.


ANSWER FOR EXERCISE 8 – EXPERIMENT 2

1. The constants: type of animal, shape of maze, strength of light source, environmental temperature

2. MV : the amount of training

3. RV : the length of time a learned behaviour persisted

4. If the amount of training is increased, then the length of time a learned behavior persisted will also increase.


A TEACHER’S REFLECTION….”The most common problem is that students write a simple statement that is a cause and effect relationship that makes a prediction (example: "If I eat chocolate, then I will get pimples."). They have to be reminded that what makes a hypothetical statement is the idea that two things might be, but not necessarily related. In other words they failed to state a proposed relationship before making the prediction. Literally speaking, cause and effect statements are based on unstated assumptions. In models for scientific research, minimizing assumptions first and then stating your hypothesis is how variables are controlled.”……


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3 Constructing Hypotheses

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