The method and the results are on the energy transfers lab. Do the analysis yourself first, then check the answers below.
Quick answer: An energy transfer is the movement of energy from one store to another or its change from one form to another. These answers go with the grade 7 science lab on energy transfers: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
These model answers use the sample table. Your own values will differ slightly, but the efficiency should stay roughly constant at about 60 % and the wasted energy should be larger for higher drops.
Level: Grade 7 science (Year 8 · Class 7) · Curriculum: MS-PS3-5
Question 1 Variables
1. The drop height.
2. The bounce height.
3. A throw would give the ball extra kinetic energy at the start, so the energy at release would no longer depend only on the height.
Question 2 Energy before and after
GPE = m × g × h with m × g = 0.057 × 9.8 = 0.5586 N.
(a) 0.5586 × 1.00 = 0.56 J.
(b) 0.5586 × 0.61 = 0.3407 J = 0.34 J.
Question 3 Wasted energy
Wasted = 0.5586 − 0.3407 = 0.2179 J = 0.22 J.
It was transferred as thermal energy to the ball and floor and as sound when the ball hit the floor.
Question 4 Efficiency of the bounce
The mass and g cancel, so efficiency = bounce height ÷ drop height × 100.
0.40 m: 0.24 ÷ 0.40 = 60 %. 0.60 m: 0.36 ÷ 0.60 = 60 %. 0.80 m: 0.49 ÷ 0.80 = 61 %. 1.00 m: 61 %. 1.20 m: 0.72 ÷ 1.20 = 60 %.
Question 5 Graph
The points lie on a straight line through the origin, so bounce height is proportional to drop height.
Gradient = 0.72 ÷ 1.20 = 0.60. It equals the efficiency as a fraction.
Question 6 Prediction
Bounce height ≈ 0.60 × 1.50 = 0.90 m.
Energy at the start = 0.5586 × 1.50 = 0.838 J. Energy kept = 0.5586 × 0.90 = 0.503 J. Wasted = 0.838 − 0.503 = 0.34 J.
Question 7 Reliability
The range is 0.50 − 0.48 = 0.02 m.
Improvements: film at a high frame rate and read the highest frame, keep the camera level with the rule to avoid parallax, and repeat more times.
Question 8 Different balls
The efficiency would be lower. A soft ball deforms more at impact and transfers more energy as thermal energy and sound, so less is left as kinetic energy for the bounce.
