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Investigation into Centripetal Force or why things go in circles

The Experiment You will need the following equipment –A piece of string –A Rubber Bung –A Biro tube –Some 100g and 10g masses –Weighing scales –IPad to record results Use scales to make M 1 = m 2

What you are going to do You are going to work in pairs. One of you needs to - Measure the mass of the bung m 2 and place a mass M 1 on the end of the string approximately equal to 1.5 m 2 (40-50g) - Pick a length of string to be hanging out of the string holder (Biro tube). You can keep track of what this length is by putting a piece of tape at the bottom of the string holder. - Make sure while you are swinging the stopper that the tape stays stationary but does not touch the glass. - Practice getting the thing swinging concentrate on making sure the tape stays constant and the angle between the string and the string holder stays at approx 45 o See Example Video

What you are going to do - The other person needs to set up a table on the IPad. - To do this open up the Spread Sheet App on the Ipad. - In column A put the heading R for Radius - In columns B, C and D put the heading T for Time period - In column E put the heading Mean T - In column F put the heading T 2 for Time period squared - You will record the results in this table as it will make it easy to work out a mean and to plot a graph by clicking the graphs tab at the top.

What you are going to do - You are now ready to start the experiment. - While one of you swings the bung around as previously described the other person should count 10 or so periods and time it. - Repeat this process 3 times and calculate the mean to reduce the uncertainty. - make sure you record these results in the table on your IPad - Change the length of the string and do it again. - Do this for different lengths of string. - Make a graph of time period squared vs r = distance between bung and string holder (Biro Tube).

What does this all mean If the angle is 45 o then F grav = F centripetal This means F centripetal = m 2 g F Centripetal Note: g = approx 10N/Kg

What does this prove From this we can prove that F = m 2 v 2 / r using a bit of algebra F = m 2 v 2 / r can be rearranged to v 2 = r F / m 2 Previously we worked out F = 10m 2 Therefore F / m 2 = 10 and this means v 2 = 10r T = 2πr / v can be rearrange to v = 2πr / T v 2 = 4πr 2 / T 2 substitute for v 2 and we get 10r = 4πr 2 / T 2 Therefore T 2 = 1.25 r Hopefully the slope of our graph is approximately 1.25

Physics in real life Physicists in the past used these types of experiments to work out relationships between forces, and objects. Johannes Kepler predicted the orbits of planets

Physics in real life They used this understanding to develop laws and theories that allowed humankind to achieve great things. Isaac Newton’s laws got us to the Moon

Physics in real life In A Level Physics we help develop your ability to spot connections and solve problems. These are key skills to be successful in all businesses not just science.

Course Structure In year 12 you do the AS Physics modules Unit 1 – Particles, Quantum Phenomena and Electricity Unit 2 – Mechanics, Materials and Waves In year 13 you do the A2 Physics modules Unit 4 – Fields and Further Mechanics Unit 5 – Nuclear Physics, Thermal Physics & Option Option Topic – Turning Points which includes –The discovery of the electron –Wave Particle Duality –Special Relativity 4 hrs lessons + 4 hrs independent study per week

Exams and Coursework