P5 Practical Flashcards
(29 cards)
Force and Elasticity Practical
Aim
To investigate the relationship between force and extension of a spring.
Method steps
- Clamp a spring vertically using a clamp stand.
- Add a ruler beside the spring to measure extension (starting from zero).
- Measure the spring’s original length (no force added).
- Add a mass (e.g. 100g = 1N) and record the new length.
- Repeat by adding more masses (e.g. 1N, 2N, 3N, etc.).
- Record force applied (N) and extension (cm or m).
- Calculate extension:
Graph – What Should It Look Like?
• A straight line through the origin = obeys Hooke’s Law
• Line starts to curve = elastic limit exceeded (spring won’t return to original shape)
Plotting force vs length instead of extension
Plot force vs extension, not full length
Using grams instead of newtons
100g = 1N (use W = mg if needed)
Confusing elastic limit with spring constant
Elastic limit = point where it stops obeying Hooke’s Law
What is Hooke’s Law
The extension of a spring is directly proportional to the force applied, up to the elastic limit.
Equation for Hooke’s Law?
F = k x e
What is meant by ‘elastic limit’?
The point where a spring will no longer return to its original shape
How do you calculate extension?
New length – original length
What does a force vs extension graph look like for Hooke’s Law?
A straight line through the origin.
Why should the ruler be at eye level?
To avoid parallax error when reading extension.
Unit of extension in Hooke’s Law formula?
Metres (m) — not cm!
Aim of the Practical INVESTIGATION OF MOTION
To investigate how the motion of a trolley changes when the force applied to it is varied or when the mass is changed.
APPARATUS NEEDED
• Trolley
• Pulley
• String
• Mass hanger and slotted weights
• Clamp stand
• Ramp or runway
• Light gates and data logger (preferred) OR a stopwatch (less accurate)
• Ruler or metre stick
• Balance (to measure mass of trolley)
Step-by-Step INVESTIGATING MOTION
- Place a trolley on a flat ramp or low-friction track.
- Attach a string to the trolley. Pass the string over a pulley at the end of the bench.
- Attach a mass hanger to the other end of the string so it hangs freely.
- Set up a light gate connected to a data logger to accurately measure the trolley’s acceleration.
- Measure the mass of the trolley and record it. Keep it constant throughout.
- Vary the mass on the hanger to change the force pulling the trolley.
• Start with 1 weight (e.g. 100g = 1N), then 2 weights, 3, etc. - Each time:
• Release the trolley from rest.
• Use the light gate to measure acceleration as it passes through. - Repeat each reading at least three times and take the mean acceleration.
- Record the force applied (weight = mass × gravity) and the acceleration.
- Plot a graph of force (N) on the x-axis and acceleration (m/s²) on the y-axis.
Effect of Mass on Acceleration
- Keep the force (hanging weight) the same.
- Start with a light trolley.
- Add masses onto the trolley, not the hanger.
- Each time, measure the acceleration using the light gate.
- Plot a graph of mass (kg) on the x-axis and acceleration (m/s²) on the y-axis.
Expected Graphs and Relationships
• Should be a straight line through the origin
→ Acceleration is directly proportional to force
→ Proves Newton’s Second Law
Newton’s Second Law:
• F = force (N)
• m = mass (kg)
• a = acceleration (m/s²)
Confusing speed with acceleration
Use acceleration, not just how fast
justify why light gates are better than stopwatches:
• More precise
• No reaction time errors
• Automatically calculate acceleration
What is the aim of the motion practical?
To investigate how acceleration is affected by the force or the mass of a trolley.
What is Newton’s Second Law equation?
F= m x a
