NAME: Brandon Sookdeo DATE: Monday 6th January TITLE: Planning and Design PROBLEM
STATEMENT: It is sometimes said that ‘The flight of a golf ball is determined more by air resistance than by gravity’. This is because when the golf ball is moving quickly the drag force acting on the ball is larger than the weight of the ball. This statement can be investigated in the laboratory by reversing the situation using a stationary ball in a current off air. Design a laboratory experiment to investigate how the force action on the stationary golf ball due to air flowing past it varies with speed of the air.
HYPOTEHSIS: The flight of a golf ball is determined more by air resistance than by gravity. AIM: To investigate how the force acting on a stationary golf ball due to air flowing past it varies with the speed of the air.
MATERIALS
APPARATUS: - Golf ball
- Top pan balance
- Newton meter (spring balance) - Airspeed indicator
- Wind pipe with fan mounted at one end - Thin string
DIAGRAM:
Fig.1 Diagram showing setup of apparatus to investigate whether the flight of a golf ball is determined more by air resistance than by gravity.
THEORY: Whenever a solid body moves through a fluid, that is a liquid or gas, the fluid resists motion. The object or body is subjected to an aerodynamic force, known as the drag force, which acts in a direction opposing the motion of the body. This force is generated as a result of the difference in velocity between the solid object and the fluid, between which there is motion. Drag force, or the force of air friction for a falling body, increases with speed. An object which is falling in a fluid will eventually reach a speed at which the force of air friction is equal and opposite to the force of gravity. Here, the object no longer accelerates but has constant speed. This speed with its direction is referred to as terminal velocity. Hence, drag force can be referred to as a resistive force which opposes the motion of the object. Drag is most common in frictional forces which act parallel to the object’s surface, as well as pressure forces which act perpendicular to the object’s surface, referred to as Lift. Factors which affect the drag force include: the speed of the object, the material of the object, the viscosity of the fluid and rotation as well as aerodynamics of the object.
During the flight of a golf ball, projectile motion is experienced. The forces acting on it as it moves through the air is shown above. It is possible to investigate whether the flight of a golf ball is determined more by air
resistance than by gravity based on the principles that the forces which exist are- Weight, Tension and Drag. Weight is the downward force acting on the ball due to gravity and is the product of the ball’s mass (m) and the
gravitational field strength (g). Tensional forces occuring in the string oppose the motion of the ball downwards. Both forces moving in opposite directions are balanced. Wind velocity opposes the downward force exerted by the golf ball. The drag force can be calculated using the formula:
PROCUDURE: 1. Using the top pan balance, measure and record the mass of the golf ball. 2. Set up the apparatus as illustrated in the diagram above.
3. Ensuring that the fan is turned off, take the initial reading of the spring balance with the ball.
4. Turn the fan on at a speed of 5ms-1 and record the reading on the spring balance.
5. Repeat Step 4, increasing the wind velocity each time by 5ms-1 until a speed of 30ms-1 is reached.
6. Repeat Steps 1-5.
7. Place all data obtained in Table 1 and using data collected, plot a graph of drag force against velocity.
VARIABLES: Constant variables: - Mass of golf ball
- Apparatus used during the experiments - Position of ball
Manipulating variables: - Velocity of the air Responding variables:
- Drag force acting on the ball due to the air
EXPECTED
RESULTS:
Table 1: Results obtained in the experiment investigating whether the flight of a golf ball is determined more by air resistance then by gravity
Graph of Drag force against wind velocity. Wind
Velocity/ms-1 Weight/ N Average Weight / N, F+F/2 Drag Force/ N Initial Weight- Average Weight 1st Trial, F 2nd Trial, F 0 5 10 15 20 25 30
TREATMENT OF RESULTS:
Plot a graph of Drag force vs Airspeed and from the graph, read off range of values for which drag force is greater than weight of ball. If this range of values falls within average speed of golf ball in air determined ,then it can be concluded that a golf ball in air’s drag force is greater than its weight and hence its flight is determined more by drag force than by weight and the hypothesis is true. If this range of values does not fall within average speed of golf ball in air determined then it can be concluded that a golf ball in air’s drag force is less than its weight and hence its flight is determined more by weight than by drag force and the hypothesis is false.
PRECAUTIONS: 1. Zero all scales before use so as to reduce systematic errors and allow for accuracy.
2. Ensure that wherever this lab is being conducted that there is no wind interference so that the only force acting on the ball is due to air speed. SOURCES
OF ERROR: 1.Parralax error when taking reading may result in inaccurate readings. 2. External factors such as wind and vibration interferences may result in inaccurate readings.
