Exam - Experimental Skills Flashcards
Why might a scientist find experimental results unbelievable?
- The original theory might be supported by results from other experiments
- Cannot believe that the original theory is wrong
- The original theory is the basis for other ideas
Suggest some reasons that scientists might decide to publish their results.
- To allow peer review of data
- To assess the reproducibility of the data
- To promote further enquiry
- To encourage other scientists to produce new theories
What is a systematic error?
An error that is the same every time the experiment is performed (for example, if the time measured was always 0.5s too short)
What is a random error?
An error that is not the same every time the experiment is performed (for example, if the time measured was only accurate to plus or minus 0.5s, completely at random)
When writing up an experiment, what must you include?
- An equation
- Mention that you measure each of the things in the equation (other than the thing you are trying to find)
- Mention a piece of equipment used to measure EACH measurement (e.g. a measuring tape for distance)
- REPEAT the experiment and TAKE AN AVERAGE
- Mention some sort of experimental detail
Why do we take repeat readings?
- To calculate the mean
- To spot anomalies
- To reduce the effect of random errors?
Is it true that repeating readings improves accuracy?
No! Repeating readings reduces RANDOM errors, but doesn’t do anything to SYSTEMATIC errors, that might mean that the reading is still inaccurate.
How do you describe the shape of a graph?
or:
How do you describe the relationship between two variables on a graph?
- Say something simple about the relationship between the variables, for example “As X increases, Y also increases”
- Say whether the graph is LINEAR (a straight line) or NON-LINEAR (not a straight linear)
What is a CONTROL variable?
A variable that you keep the same in order to make the experiment a fair test.
What is the INDEPENDENT variable?
The variable that YOU change.
What is the DEPENDENT variable?
The variable that changes in response to the thing you change.
Describe an experiment to find the speed of a travelling object (e.g. a bike around a velodrome)
- Speed = Distance / Time
- Measure the DISTANCE using a MEASURING TAPE
- Measure the TIME using a STOPWATCH
- Detail about the experiment (e.g. Start the stopwatch as the front wheel of the bike first crosses the finish line, stop it when the front wheel of the bike crosses again)
- Repeat and take an average
- Use the equation to find the average speed
Describe an experiment to find the density of a regular solid (e.g. a cube)
- Density = Mass / Volume
- Measure the MASS using a MASS BALANCE
- Find the VOLUME by measuring the LENGTHS of the shape using a RULER, then use an equation to calculate the volume (e.g. find the length of the side of a cube then cube it to find the volume)
- REPEAT and take an AVERAGE
- Use the equation to find the density
Describe an experiment to find the density of an irregular solid (e.g. a paperclip)
- Density = Mass / Volume
- Measure the MASS using a MASS BALANCE
- Find the VOLUME by using the DISPLACEMENT METHOD
- Displacement Method: Fill a measuring cylinder up part of the way and record the volume in the cylinder. Place the object into the measuring cylinder. Measure the new volume. The volume of the object is the difference between the two.
- REPEAT and take an AVERAGE
- Use the equation to find the density
Describe an experiment to find the pressure produced by a human
- Pressure = Force / Area
- Measure the FORCE by finding the MASS of the person using a MASS BALANCE, then multiplying by 10 to produce the weight (using W = mg)
- Measure the AREA by placing a shoe on a piece of graph paper, drawing around it, then counting the number of squares inside the outline. Then multiply by the area of one square, then multiply by two (as you have two feet.
- REPEAT and take an AVERAGE
- Use the equation to find the pressure
