The method and the results are on the newton's laws lab. Do the analysis yourself first, then check the answers below.
Quick answer: Newton's three laws describe how forces change motion. These answers go with the Physics 9-10 lab on newton's laws: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
These model answers use the sample data in the results table. Your own results will differ a little, but the shape of the graph and the main conclusions should agree. Always show the equation, the substitution and the unit.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS2-1, GCSE P5
For uniform acceleration from rest, d = ½ a t². Multiply both sides by 2: 2d = a t². Divide by t²: a = 2 d ÷ t².
Question 3 Plot and describe
The points lie close to a straight line through (or very near) the origin. This shows that acceleration is directly proportional to the resultant force when the mass is constant.
Question 4 Gradient and mass
Gradient = (1.49 − 0.29) ÷ (0.980 − 0.196) = 1.20 ÷ 0.784 = 1.5 m/s² per N. Gradient = 1 ÷ m, so m = 1 ÷ 1.5 = 0.66 kg. This is about 10 % above 0.600 kg; the string, pulley wheel and friction make the system behave as if it were heavier.
Question 5 Why the total mass stays fixed
The force that pulls the system is m × g of the hanging mass. If masses were only added to the hanger, the total mass would change too, and both force and mass would vary together. Moving masses keeps the total mass constant, so only the force changes.
Question 6 Is the force really m × g?
T = m (g − a) = 0.100 × (9.8 − 1.49) = 0.100 × 8.31 = 0.83 N. The weight is 0.980 N, so the string tension is smaller than the weight, because the hanger accelerates downwards.
Question 7 Timing uncertainty
Percentage uncertainty in t = 0.05 ÷ 1.16 × 100 = 4.3 %. Because a depends on t², the uncertainty in a is double: about 8.6 %.
Question 8 Improve the investigation
Any two: use light gates and a data logger for more precise times; repeat each timing more times; tilt the runway slightly to compensate for friction; use a longer track; use a lighter pulley; check the pulley and string run freely. Two reliable improvements are enough if each is justified.
