Tennis is played on a rectangular flat surface, usually of grass, clay, or concrete (hard court). The court is 78 feet (23.77 m) long, and its width is 27 feet (8.23 m) for singles matches and 36 feet (10.97 m) for doubles matches. Additional clear space around the court is needed in order for players to reach overrun balls. A net is stretched across the full width of the court, parallel with the baselines, dividing it into two equal ends. The net is 3 feet 6 inches (1.07 m) high at the posts, and 3 feet (914 mm) high in the center. The mesh ("holes") of the net may be of any shape, but must be small enough to prevent a tennis ball from going through the net. Since the ball is approximately 2-1/2" wide, the mesh must be smaller than that. The court on the right side of each player is called the deuce court, while the left side is called the ad court. The area need for a tennis court is 120' by 60' oriented north-south. A narrow court can be 120' - 55'.

The lines are typically 1"-2" wide, but the baselines may be up to 4" wide. All lines must be within the court boundaries (i.e., the outermost edge of the line must be within the court).

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78 feet in length and 27 feet wide for singles and 36 feet for doubles

There are four different strokes used in Olympic swimming: freestyle, breaststroke, butterfly and backstroke.

The programs for men and women are the same, except that the longest race for men is the 1500m while the women's longest race is the 800m.

In addition to individual events for each of these strokes, individual medley events and relays are contested.

Medley events utilise all four strokes. In the 200m individual medley, competitors swim 50m of butterfly, followed by 50m backstroke, 50m breaststroke and 50m freestyle.

The order is the same for the 400m individual medley, with competitors swimming 100m of each stroke.

In the 4x100m medley relay, the race begins with backstroke, then breaststroke, butterfly and freestyle.

In freestyle and backstroke, swimmers may touch the wall at the end of the pool with any part of their bodies, so most perform tumbleturns, somersaulting in front of the wall and pushing off it with their feet.

However, in individual medley events, swimmers must touch the wall with their hands at the end of the backstroke leg before switching to breaststroke.

Breaststroke and butterfly swimmers have to touch the end of the pool with both hands at the end of each lap, therefore the tumbleturn is not possible.

For breaststroke, freestyle, butterfly and individual medley events, swimmers begin the race by standing on blocks at the end of the pool.

Swimmers are given a warning before a loud beep sounds to start the race.

A false start results in disqualification at the Olympics.

All timing is electronic - pressure pads in the blocks and the wall at the end of the pool register when swimmers have begun and finished their races.

In relays, a team is disqualified if a member of the team leaves the blocks more than 0.03 of a second before the team member in the water touches the wall.

Olympic events take place in a 50m pool, meaning events longer than 50m require laps to be swum.

The pool at the Sydney International Aquatic Centre is three metres deep and has 10 lanes, although only eight will be used for racing. One lane at either side of the pool will remain vacant.

Water in the Olympic pool is regulated to be between 25ºC and 27ºC.

Any stroke is permitted in freestyle events, but all competitors choose the crawl stroke in these events because it is the fastest stroke. Because of this, the crawl stroke has become known as freestyle.

When swimming freestyle, some part of the body must remain above the water at all times.

The exception is when swimmers start the race and make turns at the end of each lap.

At these times swimmers are allowed to remain submerged for 15 metres.

Butterfly

Butterfly was "invented" for the 1956 Games after some swimmers had begun to exploit a loophole in the breaststroke rules by lifting their arms out of the water.

Like breaststroke, butterfly is swum face down, but some swimmers now breathe to the side, rather than by looking out in front of them.

The kick is a vertical one, and both feet must be moved together.

The arms must be swung forward together.

At the end of each lap, both hands must touch the wall together.

Backstroke

Backstrokers must swim on their backs with their faces towards the sky.

They are allowed a degree of body rotation as they swim.

Both the swimmer's feet must be under the water at the start. After starting, the swimmer can remain underwater for 15 metres.

Breaststroke

This stroke requires swimmers to swim face down, moving their arms and legs at the same time in a horizontal plane.

After each turn, and at the start, swimmers are allowed to make one arm stroke and leg kick while underwater.

The swimmer's head must break the surface during each complete stroke.

Like the butterfly, the swimmer must touch the end of the pool with both hands at the end of each lap.