University Physics I · topic UPI-09.07
Rolling kinematics
Connect the ideas, make your working visible, and test the result. Use the hints when you need a starting point; open the full solution after your attempt.
Further practice
Work through a fresh case before tackling the extension.
Rolling Kinematics: predict a finite change
Rolling without slipping is combined translation and rotation in which the point of the body touching the surface has, at that instant, the same velocity as the surface, which on a fixed road forces v_cm = Rω. Use the supplied topic model Y_out = v/w, where Y_out is v = 0 POINT BELOW AXLE (m). The output symbol Y_out is distinct from all input symbols. ^ denotes a power; π = 3.141592653589793. w is Spin rate ω, clockwise, measured in rad s⁻¹. Keep v (Axle speed v_cm) = 1.5 m s⁻¹; phi (P, angle round from the top) = 60 ° fixed. For this exercise use only 4.53125 rad s⁻¹ ≤ w ≤ 8.46875 rad s⁻¹ on this continuous branch. A grid of test settings is an input restriction for this exercise, not by itself a claim of physical quantisation. This calculation retains the topic model's stated assumptions; it does not extend them to a different physical setup. Calculate Y_out at w = 5.3975 rad s⁻¹ and 5.94875 rad s⁻¹. Find the signed output change ΔY_out and the average sensitivity ΔY_out/Δw across this interval. State whether the response increases or decreases; distinguish this interval average from a derivative at one point.
v = 0 POINT BELOW AXLE against w
Predictions from the supplied Rolling Kinematics model, with all other inputs fixed as stated in the question. 5 calibration points support a trend comparison; they are not measured data or a straight-line law.
Vertical axis (y): v = 0 POINT BELOW AXLE / m
Horizontal axis (x): w: Spin rate ω, clockwise / rad s⁻¹
Axes show the supplied calibration interval; the origin may lie outside the plot.
Read the exact data as a table
| w: Spin rate ω, clockwise / rad s⁻¹ | v = 0 POINT BELOW AXLE / m |
|---|---|
| 4.53125 | 0.3310344827586207 |
| 5.515625 | 0.2719546742209632 |
| 6.5 | 0.23076923076923078 |
| 7.484375 | 0.20041753653444677 |
| 8.46875 | 0.17712177121771217 |
These are the supplied values, not a worked answer. No fitted trend is drawn.
Show a hint
Substitute each value of w separately while keeping every other input fixed, then subtract in the same order.
Reveal the worked solution
- At w = 5.3975 rad s⁻¹, substitute into Y_out = v/w: Y₀ = 0.277906 m.
- At w = 5.94875 rad s⁻¹, the same fixed-parameter model gives Y₁ = 0.252154 m.
- Signed change: ΔY_out = Y₁ − Y₀ = -0.0257526 m; the input change is Δw = 0.55125 rad s⁻¹.
- Average sensitivity is ΔY_out/Δw = -0.0467168 m per rad s⁻¹. Its negative sign means that this response decreases over the specified interval.
- This is a secant slope between two settings. It equals a point derivative only for a locally linear relation or in a justified small-interval limit.
Answer Y₀ = 0.277906 m, Y₁ = 0.252154 m; ΔY_out = -0.0257526 m; average sensitivity = -0.0467168 m per rad s⁻¹.
Compare the assumptions, method and units with your attempt. Explain any correction before trying another question.
Extra challenging questions
Work through the linked stages and explain what each result means.
Rolling Kinematics: infer an input with uncertainty
Rolling without slipping is combined translation and rotation in which the point of the body touching the surface has, at that instant, the same velocity as the surface, which on a fixed road forces v_cm = Rω. Use the supplied topic model Y_out = v/w, where Y_out is v = 0 POINT BELOW AXLE (m). The output symbol Y_out is distinct from all input symbols. ^ denotes a power; π = 3.141592653589793. w is Spin rate ω, clockwise, measured in rad s⁻¹. Keep v (Axle speed v_cm) = 1.5 m s⁻¹; phi (P, angle round from the top) = 60 ° fixed. For this exercise use only 4.53125 rad s⁻¹ ≤ w ≤ 8.46875 rad s⁻¹ on this continuous branch. A grid of test settings is an input restriction for this exercise, not by itself a claim of physical quantisation. This calculation retains the topic model's stated assumptions; it does not extend them to a different physical setup. A reading gives Y_out = 0.21635265 m, with a bounded reading uncertainty ±0.0058846 m. Treat the model and all fixed inputs as exact for this exercise; the bound is not a standard deviation. First estimate the unknown w by straight-line interpolation between the two endpoint predictions. Then solve the actual model on the stated branch to an absolute input tolerance of 0.00039375 rad s⁻¹, using a numerical bracket if required. Find the full input interval consistent with the bounded reading uncertainty and compare it with a symmetric input-error assumption. Do not assume that the supplied calibration points prove monotonicity outside this branch.
v = 0 POINT BELOW AXLE against w
Predictions from the supplied Rolling Kinematics model, with all other inputs fixed as stated in the question. 5 calibration points support a trend comparison; they are not measured data or a straight-line law.
Vertical axis (y): v = 0 POINT BELOW AXLE / m
Horizontal axis (x): w: Spin rate ω, clockwise / rad s⁻¹
Axes show the supplied calibration interval; the origin may lie outside the plot.
Read the exact data as a table
| w: Spin rate ω, clockwise / rad s⁻¹ | v = 0 POINT BELOW AXLE / m |
|---|---|
| 4.53125 | 0.3310344827586207 |
| 5.515625 | 0.2719546742209632 |
| 6.5 | 0.23076923076923078 |
| 7.484375 | 0.20041753653444677 |
| 8.46875 | 0.17712177121771217 |
These are the supplied values, not a worked answer. No fitted trend is drawn.
Show a hint
The model's endpoint predictions bracket the reading. Solve Y_out(w) = Y_measured and then solve again at Y_measured − u and Y_measured + u; a nonlinear inverse can give unequal input deviations.
Reveal the worked solution
- Endpoint predictions are Y_out(4.53125) = 0.331034 m and Y_out(8.46875) = 0.177122 m. The target lies between them. On the selected branch the response is strictly decreasing.
- Endpoint interpolation gives w_line = 4.53125 + (0.216353 − 0.331034)(8.46875 − 4.53125)/(0.177122 − 0.331034) = 7.46512 rad s⁻¹. This estimates the inverse of the endpoint chord, rather than assuming that chord is the physical model.
- Use the actual equation, not the chord, and bracket its root. Evaluating the midpoint and retaining the sign-changing half-interval gives w = 6.93313 rad s⁻¹; substituting back gives Y_out = 0.21635265 m.
- The interpolation error in the input is |w_line − w| = 0.531994 rad s⁻¹. This is larger than the requested numerical tolerance.
- Invert both limits Y_out = 0.21046805 m and 0.22223725 m. Sort the roots even if the response decreases: 6.74954 rad s⁻¹ ≤ w ≤ 7.12697 rad s⁻¹.
- The lower and upper input deviations are 0.183582 rad s⁻¹ and 0.193847 rad s⁻¹. They differ because the inverse response is nonlinear; a symmetric error bar would only be a local approximation. This interval includes reading uncertainty only, not model error or uncertainty in fixed inputs.
Answer w ≈ 6.93313 rad s⁻¹; compatible interval [6.74954, 7.12697] rad s⁻¹. Endpoint interpolation gives 7.46512 rad s⁻¹.
Compare the assumptions, method and units with your attempt. Explain any correction before trying another question.