Forces levels 7-9 Flashcards
Explain how you would determine the size and direction of this vector on a scale diagram
- Measure the length of the force and use the scale to work out what the size of the force is
- Use a protractor to measure the angle that the force is at to give you the direction
a) it can be mesured in degress clockwise or anticlockwise from the horizontal or vertical as long as it is clearly states
b) You can measure it as a bearing from the vertical. Barings are always measured in a clockwise direction and have values from 0-360 degrees
Draw a scale diagram to represent a vector that is at a bearing of 050 degrees and has a magnitude of 75N. Select an appropriate scale for your diagram.
Explain how to investigate the effect that a resutant force has on the accleration of an object
- Set up the equipment as shown in the diagram
- Measure the total mass of the masses and the trolley together. The total mass is a control variable and must be kept the same throughout the experiment. This is because the acceleration of a body depends on the force but also on the mass
- move 100g of the masses from the trolley to the end of the string. The weight force acting on the mass will be transferred through the string to the trolley
- Calculate the size of the weight force that is acting using the formula: weight = mass x gravitational field strength
- let the trolley go and use the light gates to measure the speed of the trolley through each gate
- measure the distance between the light gates and use the formula:acceleration = change of speed/time to find the acceleration of the trolley
- Now move another 100g mass from the trolley to the string and repeat the experiment with 200g total mass. Continue to change the mass on the string in 100g intravals up to a maximum of 600g.
- Plot a graph of force (x-axis) against acceleration (y-axis). The gradient of the graph will be the combined mass of the trolley and the masses
What are the most likely sources of error when using a plumb bob to find the centre of mass of an object.
- Friction between the card and the pivot stopping it from hanging exactly with the centre of mass below the point of suspension
- Friction between the card and the plumb bob stopping it from hanging exactly with the centre of mass below the point of suspension
- Movement of the card or the plumb bob when drawing the vertical line, preventing the line from being entirely accurate
Explain how you would investigate the stability of an object
- Set up the equipment as shown in the diagram
- Ensure that there is a rough surface on the slope so that the object will topple over and not slide down the slope
- Gradually increase the angle of the slope and stop increasing it when the object starts to topple over
- Repeat the experiment 3 times and take an average
- Repeat the experiment with a range of different objects
Explain how you can investigate how changing one force of three forces that are in equilibrium affects the angle between them.
- Set up the equipment as shown in the diagram
- The weight force from each of the sets of masses is transferred to the centre point. W3 pulls down while W1 and W2 pull upwards and to the side. Work out the forces that are acting on the centre point of the three strings using the formula:
Weight = mass x gravitational field strength
- measure the angles made by each of the side strings with the horizontal one
- Draw a scale diagram to prove that the forces form a complete circle, proving that there is no resultant force
- Change the mass of one of the masses and repeat steps 1-4. This can show that the forces are still in equilibrium but that the angle changes as the relative sizes do
Explain who to reslovle two forces into horizontal and vertical components
Example calculations:
Use a scale diagram to reslove each of the forces into horizontal and vertical components.
Then add together the horizontal components of both forces and the vertical components of both forces.
Remember that if the components are acting in opposite directions you subtract them, while if the components are acting in the same direction you add the forces.
Explain how you can reslove forces into horizontal and vertical components to check that the object is in equilibrium (resultant force of zero)
Example calculation:
- For each force, use a scale diagram to resolve the forces into horizontal and vertical components
- Add up the horizontal components of all of the forces. remember that forces in the same direction add up and forces in opposite directions subtract
- Repeat step two for the vertical components
- If the both of the horizontal and vertical components add up to give a resultant force of zero then the object is in equilibrium
