3. Steps 1 、 Prepare a system like that. 2 、 Turn on the power to make the ticker time run. 3 、 Let the paper tape free-fall. 4 、 Turn off the power. 5 、 Calculate the “g” by using the dots in the paper tape if the dots are spaced so as to indicate uniformly accelerated motion. If not, repeat the steps before. We don’t use these dots
4. Pay attention that: 1 、 There are at least 6 clear dots on the paper tape. 2 、 Time between each dot is 0.02s. 3 、 We often use 5 dots as a count point so that the time between two count points is 0.1s. a 1 =(v 4 -v 1 ) / （ 3×0.1s ） a 2 =(v 5 -v 2 )/ （ 3×0.1) a 3 =(v 6 -v 3 )/(3×0.1s) average of a=(a 1 +a 2 +a 3 )/3 so average of a = g
5. Or we can make a form: 5 4 3 2 1 Average acceleration g =_________ Average Velocity(cm/s) Displacement coverd in each interval(cm) Time for each interval (s) Interval No.
6. Errors There are always some errors in the experiment: 1 、 Air resistance will affect the car's acceleration. 2 、 When we measure the displacements between dots , it may have some system errors. 3 、 When we calculate the g, if we use: a 1 =v 1 /0.1s a 2 =v 2 /0.1s ……………….. so average a = (v1+v2+v3+v4+v5+v6)/(0.1×6) it’s unaccurate.
