Investigate one factor affecting the terminal speed of spheres falling in a liquid Background: In physics, terminal velocity is when the acceleration of the object becomes constant due to the other forces around, such as gas or liquid. When the gravity force and the drag force become equal, the free falling object’s velocity is called terminal velocity. This means that the acceleration of the object is constant. When the object accelerates, the drag force increases. At certain speed, the drag force becomes same as the mass of the object. At this point, the object’s acceleration stops and it starts to free fall with the terminal velocity.

Bigger mass leads to bigger terminal velocity, however, bigger drag force leads to smaller terminal velocity. Hypothesis: If the area of the object increases, then the terminal velocity will decrease because bigger drag force leads to smaller terminal velocity. Variables: Table 1. Independent, Dependent and Controlled Variables Independent Variables Dependent Variables Controlled Variables Area of the object affected by the gravity Density of liquid Drag Coefficient (0. 47) Density of fluid (1g/cm3) Apparatus: 1 x 2m Tube 1 x Data Studio 5 x different size sphere (5cm, 10cm, 15cm, 20cm, 25cm diameter)

1 x GLX Water Method: 1. Fill up 2m tube with water. 2. Run the data studio on the laptop and set up GLX on top of the tube. 3. Place 5cm diameter sphere on top of the tube 4. Let go of the sphere and activate the GLX 5. From the data studio, state where the acceleration stopped and record down the maximum speed of the sphere. 6. Repeat stage 1 to 5, four more times to reduce uncertainties 7. Repeat stage 1 to 6 with different size of the spheres (10cm, 15cm, 20cm and 25cm diameter)

Bibliography: Glenn Elert, Allen Ma. Density of Water. 2007. 16 October 2009, hypertextbook.com.