Biomechanics: movement and impulse
הוצג| English | משמעות |
|---|---|
| base of support/beɪs ɒv səˈpɔːt/ | שטח בסיס |
| impulse/ˈɪmpʌls/ | תנופה |
What would explain this observation?
- Landing with bent knees increases the time over which momentum changes. The movement can reduce average impact force for the same momentum change.
Build the model
- Joint movement results from muscle forces acting through lever systems.
- The centre of mass and base of support 支撑面 affect stability.
- Impulse 冲量 connects force-time evidence to momentum change.
- impulse: Force integrated over time, equal to momentum change.
- base of support: The area supporting a body.
For a fixed momentum change, doubling stopping time does what to average force?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Average force = momentum change / time. Doubling the stopping time divides the same momentum change by twice the time, so the average force halves - the principle behind soft landings and follow-through.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- A biomechanical analysis must define the segment, direction and phase of movement.
- Net force and a single muscle force are not interchangeable.
- A longer lever arm can change torque without changing applied force.
In the lab: Use teacher-approved video of a safe movement with consent. Calibrate distance and time, identify frames consistently, and avoid making medical claims from a two-dimensional recording. Camera perspective can bias apparent joint angles.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: momentum changes by 150 kg metres per second.
- Average force magnitude = momentum change/stopping time.
- For 0.30 s, force = 150/0.30 = 500 N.
- For 0.60 s, force = 150/0.60 = 250 N.
- This idealized average excludes the detail of a changing force curve.
Your turn: Momentum change is 120 kg metres per second over 0.40 s. Find average force magnitude.
Momentum change is 120 kg metres per second over 0.40 s. Find average force magnitude.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 300 N. Known: momentum change 120 kg metres per second over 0.40 s. Use average force = momentum change / time. Force = 120/0.40 = 300 N. This is an average; the peak force during the interval can be higher.
Check the conclusion and its limits
- The largest force is not the same as average force.
- A school movement study should not deliberately create high-impact landings to test a prediction.
Not true: A video from one angle proves the cause of a sports injury. One camera angle shows one projection of a complex movement; forces, surfaces, fatigue and individual anatomy are invisible in it. Injury causation needs multiple views, force data and medical evidence, not a single clip.
- Joint movement results from muscle forces acting through lever systems.
- A biomechanical analysis must define the segment, direction and phase of movement.
- Watch for: the largest force is not the same as average force.
Write from an average force of 360 N
- Momentum changes by 180 kg metres per second.
- Compare the average force over 0.50 s and over 1.00 s. One camera angle does not prove the cause of an injury.
A video from one angle proves the cause of a sports injury.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
One camera angle shows one projection of a complex movement; forces, surfaces, fatigue and individual anatomy are invisible in it. Injury causation needs multiple views, force data and medical evidence, not a single clip.
Force integrated over time, equal to momentum change: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
impulse means Force integrated over time, equal to momentum change.
Momentum changes by 180 kg metres per second. What is the average force magnitude over 0.50 s and over 1.00 s, and what does one camera angle not prove?
Average force magnitude is the momentum change divided by the stopping time. A longer time spreads the same change.
What is the average force magnitude over 0.50 s?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
180 divided by 0.50 is 360 N. The one-second interval gives 180 N. Other options — 180 N (the force over 1.00 s); 180 kg metres per second (the momentum change).