Forces — OCR GCSE Physics
Test yourself on Forces with OCR GCSE practice questions.
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Forces explained
Accurate practical work depends on choosing the right instrument for each quantity and recording readings with sensible precision.
Read the full explanation
Use a ruler or metre rule for length in millimetres or centimetres, and calculate area from measured lengths, for example length × width for a rectangle, giving cm² or m². Use a balance for mass in grams or kilograms, a stopwatch or timer for time in seconds, a measuring cylinder or burette for volume in cm³ or ml, and a thermometer for temperature in degrees Celsius. Read scales at eye level to avoid parallax error, note the smallest division to judge precision, and repeat readings where possible. Record every value with its unit and an appropriate number of significant figures.
Use of appropriate apparatus to measure and observe the effects of forces including the extension of springs.
This practical activity asks you to choose suitable apparatus and use it to measure and observe how forces change a spring. A common method hangs a spring from a clamp and boss on a retort stand, attaches a mass hanger, and records the position of a pointer against a ruler before adding masses in equal steps. You calculate the force from the weight of each mass using W = m × g, where g is about 9.8 N/kg on Earth, and find the extension by subtracting the original length from the new length. You observe that, up to a limit, doubling the force roughly doubles the extension, and you note where the spring stops obeying this pattern. Choosing appropriate apparatus means selecting a ruler with a suitable resolution, a spring that does not permanently deform, and masses that give a measurable but safe range of forces.
Your focus
- Choose suitable apparatus for measuring length, area, mass, time, volume and temperature.
- Record measurements accurately with correct units and appropriate precision.
- Explain how to reduce errors such as parallax when taking readings.
Show all 6 objectives
- Select apparatus suitable for measuring force and spring extension.
- Calculate force from mass and find extension from length measurements.
- Describe how to observe and record the effect of forces on a spring reliably.
Forces exam tips
Marking Points
- Selects a ruler or metre rule for length and records the value with a unit such as cm or mm.
- Calculates area from measured lengths, for example multiplying length by width for a rectangle.
- Uses a balance for mass and records it in grams or kilograms.
- Uses a stopwatch or timer for time and records it in seconds.
- Reads a measuring cylinder at eye level and records volume in cm³ or ml.
- Uses a thermometer for temperature and records it in degrees Celsius.
- Selects apparatus that can measure both the force applied and the resulting extension of the spring.
- Calculates the force on the spring from the hanging mass using W = m × g with g about 9.8 N/kg.
- Finds the extension by subtracting the original length of the spring from its stretched length.
- Records repeat readings and identifies the point at which the spring stops extending proportionally to the force.
Examiner Tips
- 💡State the instrument and the unit together, for example 'metre rule, length in cm'.
- 💡Quote readings to the precision of the smallest scale division rather than adding extra digits.
- 💡Repeat a measurement and average the results to reduce random error.
- 💡State the apparatus by name and say what each item measures, for example a ruler for extension and a mass set for force.
- 💡Show the calculation of force from mass with the value of g you use, keeping units consistent.
- 💡Describe how you would check the reading is reliable, such as repeating and averaging or reading the pointer at eye level.
Common Mistakes
- Reads a measuring cylinder scale from above or below eye level; view the meniscus at eye level to avoid parallax error.
- Records a measurement without a unit; always attach the correct unit to each value.
- Chooses a stopwatch to measure length; match each instrument to the quantity it measures.
- Confuses extension with total length; subtract the original length to obtain the extension.
- Treats the hanging mass in grams as the force in newtons; convert to kilograms and multiply by g.
- Assumes the spring obeys proportionality for every force; identify the limit beyond which the pattern breaks down.