A force makes things change: the speed, direction and/or shape of an object.
Observable learning outcome:
Recognise that the motion of objects that are heavier and/or moving faster are harder to change.
Question type:
Diagnostic, two-tier multiple choice
Key words:
force, momentum
Mida ütlevad uuringud
Jõud kui liikuva objekti omadus
Jõudu seostatakse sageli liikumisega ja õpilased näevad jõudu kui millegi liikuva omadust, mis hoiab seda liikumas ja mis lõpeb, kui liikuv objekt jääb seisma. Teisisõnu ajavad õpilased sageli segamini impulssi/liikumishulka ja jõudu. Idee, et jõud on midagi, mis on objekti omadus ja mis hoiab seda liikumas, on laialt levinud (Driver et al, 1994).
Kuidas seda töölehte kasutada
Students can complete the questions individually, before discussing their answers in pairs, small groups or as a class.
You could use an electronic ‘voting system’ or mini white boards to elicit individual answers from a PowerPoint presentation.
Use discussion of the answers as an opportunity to rehearse the vocabulary. Particularly distinguish ‘forces’ as pushed or pulls that change the motion (or shape) of an object, and ‘momentum’ that makes the motion of an object harder to change.
Differentiation
Read out the questions to the class so that less able readers can think clearly about the science.
Equipment
For the class: Tennis ball (perhaps useful to illustrate a discussion)
Do it
Uuri allpool kirjeldatud situtatsioone. Vasta küsimustele.
Inerts
Sinu poole visatakse kaks tennisepalli.
Inerts
Sul on vaja need ostukärud nurga taga lükata.
Õiged vastused
1a A, b A 2a B, b C
Kuidas edasi
Question 1:
Ball 1 is harder to stop because it is going faster and has more ‘momentum’, so a bigger force is needed to stop it. The emphasis should be that a force is what changes the motion, and a bigger force is needed here because there is a bigger change necessary.
Some students might choose ‘C, it has more force’, perhaps because they have experienced faster balls hitting their hands harder – but the force of impact is not something the ball carries with it and the catcher can change the force by altering how they catch the ball. What the ball has that affects the force of impact is momentum.
Other answers are probably guesses, or for ‘E it is the same ball’ the student is likely to have missed that the balls are travelling at different speeds.
Question 2:
Trolley 2 is harder to turn because it is heavier and has more ‘momentum’, so a bigger force is needed to turn it. The emphasis should again be that a force is what changes the motion, and a bigger force is needed here because there is more stuff on the trolley to change the motion of.
For similar reasons to question 1 some students might choose ‘A, it has more force’ because if they are in collision with a heavier trolley it appears to hit them with more force. Again the size of the force of impact is not a fixed thing carried by the trolley and the size of the impact depends on the nature of the collision – and on the momentum of the trolley.
If students have misunderstandings about how the motion of objects that are heavier and/or moving faster are harder to change, it may be helpful to use a demonstration to guide them to a clearer explanation. For example, a tennis ball can be caught differently to change its force of impact; but caught in the same way a faster one will impact with a bigger force. It is important at this stage to distinguish between a force that makes things change, and (extra) momentum that is the property that makes an objects motion harder to change.
The following BEST ‘response activity’ could be used in follow-up to this diagnostic question:
Response activity: Force or momentum?
Viited
Driver, R., Squires, A., Rushworth, P. and Wood-Robinson, V. (1994) Making sense of secondary science, research into children’s ideas, Routledge, London, England.
