There are various methods for assessing football playing surfaces. Below, we introduce several common testing techniques used to evaluate different aspects of the field.
1. Ball Rebound Rate: This refers to the percentage of the ball's rebound height compared to the initial drop height when a standard football is dropped from 3 meters above the ground and allowed to bounce freely on the surface. The test helps determine the energy absorption characteristics of the surface.
The procedure involves using a standard soccer ball (with a circumference of approximately 68–71 cm and a weight of 396–453 grams). The ball is dropped from a height of 3 meters, and the maximum rebound height is measured. The formula used is:
BR = H / 3 × 100%
Where:
- BR = Ball rebound rate (%),
- H = Maximum rebound height after falling (in meters).
Refer to Figures 1 and 2 for visual representation of the test setup.
Figure 1: Football Bounce Test
1 – Standard scale; 2 – Soccer ball height; 3 – Football floor rebound height; 4 – Football test ground
Figure 2: Schematic of Football Rolling Resistance Test
R – 50cm; 1 – Height of football starting point; 2 – Test stand; 3 – Football test ground
Unit: cm
2. Rolling Resistance Coefficient: This measures how much resistance a ball encounters when rolling across the surface. One common method is the slope rolling technique. In this test, the ball is placed at a height of 1 meter on a 45-degree incline and released to roll down freely. The average distance traveled over three trials is recorded, ensuring that the test is conducted in windless conditions.
3. Friction and Traction: These properties are crucial for player movement and safety. Friction occurs between two surfaces in contact, while traction specifically relates to the interaction between a player’s shoe and the field. Artificial turf typically requires a higher coefficient of friction than natural grass to ensure stability during play.
The test involves placing a spiked shoe on a disc and pulling it tangentially using a dynamometer. The force required to initiate rotation is measured, and the traction coefficient is calculated using the formula:
U = 3F / DW
Where:
- U = Traction coefficient,
- D = Disc diameter (in meters),
- F = Torque (in Nm) at which the disc starts to rotate,
- W = Weight of the disc (in Newtons).
See Figure 3 for the equipment setup.
Figure 3: Traction Measuring Device
1 – Edge measuring instrument; 2 – Handle; 3 – Balance bar; 4 – Test ground
Unit: cm
4. Slope and Flatness: These are assessed using levels and rulers. The slope is measured according to the engineering design specifications, with an allowable error of no more than 0.3%. For flatness, a 4-meter ruler is used to measure the maximum deviation, which should not exceed 20 mm.
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