Investigating Terminal Velocity
When an object falls through a fluid it accelerates until it reaches its terminal velocity. At this speed the forces acting on it are balanced.
My task is to investigate the factors that affect the terminal velocity of a falling object.
· Mass of ball bearing
· Viscosity/density of the fluid
· Surface area of ball bearing
· Texture of the balls surface
I am going to investigate how mass affects the terminal velocity.
I think that as the mass of the ball bearing increases so does the weight of the ball bearing, which requires more friction to balance the ball bearing's weight thus making the terminal velocity increase.
I think that the mass of a ball bearing is directly proportional to the terminal velocity. This is because if the mass of ball bearing doubles so does the weight of the ball bearing, which requires twice as much friction to balance the ball bearing's weight, which then doubles the terminal velocity.
The scientific knowledge to prove my prediction is that as the mass of the ball bearing increases the weight of the ball bearing is increased that requires more friction to balance the ball bearings weight which increases the terminal velocity.
As the ball bearing accelerates the friction acting against the falling ball bearing increases which in turn balances out the forces applied to the ball bearing which reaches the terminal velocity.
The apparatus was set up as shown (in the diagram on the next page)
Two elastic bands were placed on the tube 60 cm (600 mm) apart measured to the nearest 0.1 cm. The first band placed low enough so that the terminal velocity of the ball bearing was reached before the ball bearing reached the band and the second band placed far enough apart so that there would have been a smaller percentage of error. The elastic bands were placed on the tube so that there are markers for the timing to be started and stopped on a fixed point.
A group of ball bearings were massed with an electric balance and an average of the ball bearings were taken. These ball bearings were massed so that an average mass could be calculated for each size of the ball bearings, by dividing the total mass of the ball bearings by the number of ball bearings.
The ball bearing was placed on the fluids surface and let to fall through the fluid.
A stop clock was started when the ball bearing reached the first elastic band and stopped when it reached the second elastic band.
The results were repeated three times for an accurate average time and any "strange results" were repeated to improve accuracy.
The results are shown in a table on the next page.
Average mass results
Ball Number of Balls Mass (g) (2dp) Average mass of one ball (g) (2dp)
A 60 1.80 0.03
B 30 3.37 0.11