The turning effects of forces

taught by Math Arena

Course description


This course is targeted at Singapore Cambridge GCE O level students, but is also relevant to IGCSE students and Singapore's Integrated program students.

If you've been following our course on forces, you should be familiar with how forces make objects move from place to place. But that's not all forces do. Ask anyone who's thrown a shuriken before and they'll tell you that the force you exert on it also causes it to spin. In fact, we use this turning effect from forces in levers, winches and the wheel and axle to make life easier for ourselves. So if you're interested to find out what forces have to do with spinning objects, this course is the one you want to take.

Course Content

You will learn:

  • Why the shuriken spins
  • How to calculate torque
  • What the centre of gravity is and how to find it
  • How to determine whether and object is going to topple or not
  • The principle behind those balancing toys that just don't seem to fall down
  • Other cool stuff! (Some of the videos in this course are marked as "explanation videos", which go into greater depth on the topics covered. We try to bring in out-of-syllabus concepts where possible to make things more interesting and give a more complete understanding of the topic)

A link to the full O level Physics syllabus can be found here

Course Prerequisites

You will need to know:

  • Some knowledge of forces (how to split a force into different components)
  • How to watch videos on your computer
Math Arena
Math Arena

The instructor is from Math Arena.The instructor is absolutely passionate about teaching and you'll find the lessons engaging and ultimately rewarding.

Course Curriculum

Introduction to the centre of gravity
Q18 A 1 m long uniform beam of 6 N weight is being lifted up vertically by a force F at the 75 cm mark. What is the minimum force to do so?
Q19 The diagram below shows a man of weight 800 N standing in the middle of a uniform, rigid, horizontal plank. The plank weighs 1000 N. Which one of the following diagrams shows the forces on the plank?
Q20 The below shows a non-uniform tree trunk of weight 1000 N resting horizontally on two supports at Q and S. The centre of mass of the tree trunk is at R. What downward force must be applied at P to lift the tree trunk just clear of the support at S?
Q21 A boy who weighs 500 N stands on a uniform plank with supports at P and Q. What are the upward forces acting on the plank at P and Q?
Q22 A thin uniform sheet of metal is cut into an irregular shape. It is 400 mm long, weighs 5 N and is hung at point P, halfway along it. The 3 N weight hung at Y makes it balance as shown. How far from P is its centre of gravity?
Q23 A uniform metre rod of weight 10 N leans against a smooth glass door in an equilibrium position as shown. What is the reaction force of the glass door on the rod?
Q24 A plane lamina is freely suspended from point P. The weight of the lamina is 2.0 N and the centre of mass is at C. The lamina is displaced to the position shown. What is the moment that will cause the lamina to swing?
Q25 A trap door XY of length 1.00 m and weighing 30 N is hinged at the end X. It is opened by pulling a string inclined at an angle 40° to the horizontal. What is the tension T in the string required to just lift the trap door?
Q24 explanation
Q26 A square shop sign (of side 1 m) consisting of a uniform lamina PQRS is attached to a vertical wall by a hinge at P so that S rests against the wall vertically below P. If the mass of the sign is 5 kg and normal reaction exerted by the wall at S is
Q27 A horizontal force F is applied to a cylinder weighing 100 N as shown below. Given that the radius of the cylinder is 0.5 m, what is the smallest value of F to cause the cylinder to roll up the step?
Q28 A square metal sheet has the corner (shaded) cut off. Which point will be nearest to the centre of gravity of the new sheet?