(CNN) -- Jo-Wilfried Tsonga ended Roger Federer's hopes of winning a record-equaling seventh Wimbledon title on Wednesday as the French 12th seed staged a stunning fightback to reach the semifinals. Federer appeared to be cruising into the last four after winning the first two sets, but Tsonga inflicted the Swiss world No. 3's first defeat from that vantage point in 179 grand slam matches. It was only the third time in the 29-year-old's glittering career that the 16-time grand slam champion had surrendered a two-set lead. Tsonga, ranked 19th in the world, triumphed 3-6 6-7 (3-7) 6-4 6-4 6-4 on Centre Court, serving out to love as he earned a clash with second seed Novak Djokovic. The Serbian, who beat Tsonga in the 2008 Australian Open final, ended the dream run of Australian 18-year-old Bernard Tomic. Tsonga defeated Federer for just the second time in six meetings, their first on grass. "It was amazing. I played unbelievable. It's never easy to come back against Roger. I'm so happy, it's crazy," the 26-year-old told reporters after reaching the semifinals at Wimbledon for the first time. "He's the biggest champion in the sport. He has achieved so much and is the best player in the world. To be two sets down and come back was unbelievable. I served really well. Against Djokovic I will have to come out and do the same again." Federer has now lost in the quarterfinals two years in a row, being beaten by eventual runner-up Tomas Berdych in 2010. "Jo played great. Really from start to finish I don't remember seeing a break point after I broke him in the first game," Federer said.

What Serbian player beat Tsonga in the 2008 Australian Open?

In the period before World War II, the New York Times published a vignette in their "The Talk of the Town" feature saying that Einstein was so well known in America that he would be stopped on the street by people wanting him to explain "that theory". He finally figured out a way to handle the incessant inquiries. He told his inquirers "Pardon me, sorry! Always I am mistaken for Professor Einstein." Einstein has been the subject of or inspiration for many novels, films, plays, and works of music. He is a favorite model for depictions of mad scientists and absent-minded professors; his expressive face and distinctive hairstyle have been widely copied and exaggerated. Time magazine's Frederic Golden wrote that Einstein was "a cartoonist's dream come true".

Why did Einstein pretend to be mistaken for Professor Einstein?

You know that friction also causes heat. Think about when you rub your hands together. It is friction that makes them warm. But why does this happen? Friction causes the molecules on rubbing surfaces to move faster. Faster moving particles have more heat energy. Heat from friction can be useful. Can you think of other places where you might find friction? Friction also lets you light a match. Heat from friction can also cause problems. It can cause a car to overheat. To reduce friction, oil is added to the engine. Oil coats the surfaces of moving parts. This coating of oil makes them slippery. When things are slippery there is less friction. Have you ever seen a sign that says, slippery when wet? This too has to do with friction. Water, like oil, can reduce friction. The wet surface may allow your shoes to slide more easily.
What would happen if all the oil leaked out of a running car engine?