How would you work out how fast does the car have to go?. Video Available. How much force is required to hold together a spinning galaxy?. Evidence of Dark Matter. What force will these wheels have to endure at 1000 mph?. Investigation into Centripetal Force. or why things go in circles.
Evidence of Dark Matter
or why things go in circles
You will need the following equipment
Use scales to make M1 = m2
You are going to work in pairs. One of you needs to
- Measure the mass of the bung m2 and place a mass M1 on the end of the string approximately equal to 1.5 m2 (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 45o
See Example Video
- 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 T2 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.
- 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 3 - 5 different lengths of string.
- Make a graph of time period squared vs r = distance between bung and string holder (Biro Tube).
If the angle is 45o then
Fgrav = F centripetal
F centripetal = m2 g
Note: g = approx 10N/Kg
From this we can prove that F = m2v2 / r
using a bit of algebra
F = m2v2 / r can be rearranged to v2 = r F / m2
Previously we worked out F = 10m2
Therefore F / m2 = 10 and this means v2 = 10r
T = 2πr / v can be rearrange to v = 2πr / T
v2 = 4πr2 / T2 substitute for v2 and we get 10r = 4πr2 / T2
Therefore T2 = 1.25 r
Hopefully the slope of our graph is approximately 1.25
Physicists in the past used these types of experiments to work out relationships between forces, and objects.
Johannes Kepler predicted the orbits of planets
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
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.
In year 12 you do the AS Physics modules
In year 13 you do the A2 Physics modules
Option Topic – Turning Points which includes
4 hrs lessons + 4 hrs independent study per week