# A -Level Physics: - The Physics Doctor - Home

A Level Physics: Just a moment. Objectives: Spec point 23: be able to use the equation for the moment of a force, moment of force = Fx where x is the perpendicular distance between the line of action of the force and the axis of rotation Spec point 24: be able to use the concept of centre of gravity of an extended body and apply the principle of moments to an

extended body in equilibrium Additional Skills Gained: Extra Skills Gained: Balancing moments Logic Puzzle The Monty-Hall Problem https://www.youtube.com/watch?v=9vRUxbzJZ9Y Lesson Link: Fermi Question

An arrow is shot at 40o from the horizontal, how far does it go both vertically and horizontally? Now your turn Who reckons they are the strongest in the class?! Also. A prize for anyone who can determine who I am. You really should know meIm pretty epic.

A little bit of history. https:// www.youtube.com/watch?v=0v86Yk14 rf8 10mins A new geezer A prize for anyone who can

determine who I am. You really should know meIm pretty epic. A little bit of history. https:// www.youtube.com/watch?v=9sdxiHyRr Cs 10mins

A new geezer The class must decide on the STRONGEST member of the class and the WEAKEST member. 10mins Just a moment..

Will the strongest member of the class please step forward. I propose a challenge. With your little finger. Try to push the door open. Your finger must be close to the hinge Just a moment.. Will the weakest member of the class please step forward. I propose a similar challenge.

With your little finger. Try to push the door open. Your finger must be close to the handle Moments A moment is the tendency of a force to cause rotation. It is defined by the following equation Moment (Nm) = Force (N) X Perpendicular distance (m) (from the pivot to line of action of the force)

Force applied Perpendicular Distance To get the same rotation, why was it harder to push the door from near the hinge? Flashback When forces on an object are balanced (in equilibrium), the object is either.

Flashback When forces on an object are balanced (in equilibrium), the object is either. When the moments (clockwise and anticlockwise) on an object then the object is either ROTATIONAL EQUILIBIRUM

Moments in action After the demo, pick up a smaller version of the set up and have a play. Use the knowledge you have gained to keep it balanced. Then draw a diagram of one example where its balanced taking necessary measurements Practice Questions A 2m plank (10kg) is placed upon a triangular pivot at the 1m mark. On the left hand side a 6kg mass is

placed 0.2m away from the pivot. On the other a mass is placed 0.8m away. The plank remains balanced. Calculate the mass of on the right hand side. A This time there are two masses each side. On the left is a 1kg mass 0.8m away from the pivot and a 2kg mass 0.4m away. On the right is a 2.5kg mass 0.3m

away and an unknown mass 0.8m away. Calculate the value of the unknown mass if the plank balances. Another 2m plank (10kg) is placed on a pivot as shown. On the left, mass A is placed 0.4m away from the pivot at the end of the plank. On the right, a 1.8kg mass (mass B) is placed 1.2m away from the pivot. Calculate the mass of mass A. The plank is now balanced. A

A B B C B

D Extra Challenge A 24cm spanner is used at 30o from the horizontal with a force of 20N vertically downward. What is the moment exerted on the spanner?

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