Unbalanced forces
Newton's Second Law
How to investigate experimentally Newton鈥檚 Second Law using light gates and a data logger
Resultant force and acceleration
Method
- A force that opposes or prevents movement. When work is done against friction, kinetic energy is converted into heat energy. compensated the runway so that the trolley moves at constant speed.
- Attach a length of card to the trolley. Measure the length of card with a 30 cm ruler.
- Set up light gates and the data logging software to measure acceleration from A to B. When prompted, type the length of card in cm.
- Put a 100g masses on to the mass hanger. Place 6 other 100g masses on the trolley.
- The 100g mass on the hanger acts as a resultant force of 1N accelerating the trolley along the runway. Record the force F in a suitable table.
- Release the trolley and allow the card to pass through light gates A and B. Record the acceleration.
- Repeat twice and average the acceleration.
- Move a 100g mass from the trolley to the hanger. This ensures that the mass being accelerated remains constant. Record F and repeat 6 and 7 above. Repeat for each mass in turn.
Results
It is important to record results in a suitable table, like the one below:
| Force (N) | Run 1 acceleration (m/s)2 | Run 2 acceleration (m/s)2 | Run 3 acceleration (m/s)2 | Mean acceleration (m/s)2 |
| Force (N) | |
|---|---|
| Run 1 acceleration (m/s)2 | |
| Run 2 acceleration (m/s)2 | |
| Run 3 acceleration (m/s)2 | |
| Mean acceleration (m/s)2 |
| Force (N) | |
|---|---|
| Run 1 acceleration (m/s)2 | |
| Run 2 acceleration (m/s)2 | |
| Run 3 acceleration (m/s)2 | |
| Mean acceleration (m/s)2 |
| Force (N) | |
|---|---|
| Run 1 acceleration (m/s)2 | |
| Run 2 acceleration (m/s)2 | |
| Run 3 acceleration (m/s)2 | |
| Mean acceleration (m/s)2 |
| Force (N) | |
|---|---|
| Run 1 acceleration (m/s)2 | |
| Run 2 acceleration (m/s)2 | |
| Run 3 acceleration (m/s)2 | |
| Mean acceleration (m/s)2 |
| Force (N) | |
|---|---|
| Run 1 acceleration (m/s)2 | |
| Run 2 acceleration (m/s)2 | |
| Run 3 acceleration (m/s)2 | |
| Mean acceleration (m/s)2 |
Graph
F = force; A = acceleration
Plot a graph of resultant force F in N on the y-axis against acceleration a in m/s2 on the x-axis. Draw the line of best fit.
The graph is a straight line through the origin.
This tells us that resultant force, F, and acceleration, a, are directly proportional.
If you double the resultant force acting on an object, you double its acceleration.
| Hazard | Consequence | Control measures |
| Electrical appliance (data logger and computer) | Electrical fault - fire/shock | Do not set up close to taps or sink. Check mains cable and plug are not broken, or wiring exposed before use. |
| Masses and hanger falling to floor | Objects falling on feet - bruise/fracture | Use relatively small masses and step back after releasing masses. Place bench stools as a cordon beneath the accelerating masses to prevent feet being placed beneath them. |
| Hazard | Electrical appliance (data logger and computer) |
|---|---|
| Consequence | Electrical fault - fire/shock |
| Control measures | Do not set up close to taps or sink. Check mains cable and plug are not broken, or wiring exposed before use. |
| Hazard | Masses and hanger falling to floor |
|---|---|
| Consequence | Objects falling on feet - bruise/fracture |
| Control measures | Use relatively small masses and step back after releasing masses. Place bench stools as a cordon beneath the accelerating masses to prevent feet being placed beneath them. |