Question: An aeroplane loops the loop in a verticle circle of radius 200m, with a speed of 40m/s at the top of thel oop. The pilot has a mass of 80kg. What is the tension in the strap holding him into his seat when he is at the top of the loop?. Answer: The centrifugal force outwards due to the rotation is mv^2/r = 80*40^2/200 = 640N. Since its at the top of the loop, this points upwards, in the opposite direction to gravity. The pilots mass is 80kg, and thus his weight is 80g = 800N (if you are supposed to take 9.8 or 9.81, then do so and change the numbers accordingly). This points downwards. Total force in the direction of up/down (taking down as positive) is 800-640 = 160N Thus his strap has to pull upwards with a force of 160N But, I have been taught that centripetal (centrifugal) acceleration (and therefore force) is always directed towards the centre of the circle described by the body in circular motion. Therefore, wouldn't the centripetal force act downwards (in addition to the force on the pilot due to gravity)?