Newton’s second law of motion states that the acceleration an object experiences multiplied by the mass of the object is equal to the net force acting on the object. Thus, if a given force acts on two objects of different mass, the object with the larger mass will have a lower acceleration. In the case of my experiment, the rate of descent on my helicopter, multiplied by the mass of my helicopter is equal to the total amount of forces acting on it.
If the forces acting on my helicopter give a net force which is zero, then my helicopter will not accelerate, it will continue moving at a constant velocity.
The forces on an object falling at terminal velocity are balanced. Terminal velocity occurs when the weight of an object is balanced by the drag.
Drag depends on the speed of an object- the faster it moves the greater the drag. Therefore, if one of my helicopters is moving faster than another, then it will create more air resistance.
Drag also depends on the shape of an object. A streamlined object will travel much faster than another object, and they have a lower terminal velocity.
We call the force of gravity on something its weight. Weight (N) = mass (kg) x gravitational field strength (N/kg) The gravitational field strength on Earth is around 10N/kg.
Astronauts on the moon tried an experiment suggested by Galileo. They dropped a feather and a hammer at the same time, and they landed together. Newton also tried this experiment, dropping a coin and a feather first in air, then in a vacuum. In the air the coin landed first, but in a vacuum, they landed at the same time.
The feather and the coin have a similar surface area, so when they begin to fall they should have about the same amount of drag. As they fall the air resistance on the feather soon increases to balance its weight, causing it to travel at terminal velocity. The coin, on the other hand, is heavier, so it continues to accelerate, and probably hits the ground before reaching terminal velocity.
The drag force (air resistance) is always in the opposite direction to the motion. The force of gravity is equal and opposite to the drag force.
I predict that by altering the surface area of the wings on my helicopter, I will be able to change the rate of descent by increasing and decreasing the air resistance of the wings. I think that if I increase the surface area of the wings, the amount of air resistance will increase, and my helicopter will take longer to reach the floor. If I decrease the surface area, there will be less air resistance, so my helicopter will travel faster. I also think that whilst doing my experiment, I may find the terminal velocity of one of my helicopters.
Method:
- Make a helicopter out of a piece of paper. Make the wings 11cm x 3cm each, and the base 10cm x 3cm, leaving a 1.5cm gap from the edges of the wings, like the one shown here.
- Fold one wing forwards, and the other backwards along the dotted line.
- Measure a height of 2m from the floor. Make a mark on the wall so that you know where to drop your helicopters from.
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Stand so that the first helicopter is level with the mark on the wall, and get another person to stand on the floor with a stop clock.
- Let go of the helicopter and time how long it takes to hit the floor. Record your results in a table.
- Repeat with the same sized helicopter 3 times, and then cut 1cm off the length of the wings. Repeat the experiment until the wings are 1cm long.
To keep my experiment fair-
I will use the same helicopter throughout my experiment to ensure accurate results. I will also mark a point on the wall so that I can drop my helicopters from the same height every time.
Results:
Analysis:
My results don’t show a linear pattern, the average times go down in steps, but this may have been caused by experimental errors. More of my average times are above my line of best fit than on or below it.
Evaluation:
I think that my experiment was fairly successful, as from my results I can see that my prediction is usually correct- reducing the surface area of the wings decreases the time it takes to get to the floor, because of the reduce in air resistance. If I was to do this experiment again, I would make another helicopter in a different way, because I think that that my results may have been in a more linear fashion if the helicopter spun more in the air.
