Turning effect of forces
12 flashcards to master Turning effect of forces
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Define the moment of a force.
The moment of a force is a measure of its turning effect around a pivot. It is calculated as the force multiplied by the perpendicular distance from the line of action of the force to the pivot.
A person pushes on a door handle. State one way to increase the moment the person applies to the door.
Increasing the force applied to the door handle, or pushing further away from the hinges (pivot) would both increase the moment. The moment is force multiplied by distance from the pivot.
Define the moment of a force. A mechanic uses a wrench to tighten a bolt. They apply a force of 20 N at a perpendicular distance of 0.25 m from the center of the bolt (the pivot). Calculate the moment of the force applied to the bolt.
Definition: The moment of a force is the turning effect of the force about a pivot.
Calculation:
* Moment = Force x Perpendicular distance from pivot
* Moment = 20 N x 0.25 m
* Moment = 5.0 Nm
Therefore, the moment of the force applied to the bolt is 5.0 Nm.
A door requires a moment of 12 Nm to open. You apply a force of 6 N to the door handle. State the perpendicular distance from the hinge (pivot) at which the handle must be located for you to successfully open the door.
* Moment = Force x Perpendicular distance
* Rearrange: Perpendicular distance = Moment / Force
* Perpendicular distance = 12 Nm / 6 N
* Perpendicular distance = 2.0 m
Therefore, the door handle must be located 2.0 m from the hinge for you to successfully open the door.
A 2.0 m long beam is pivoted at its center. A weight of 3.0 N is placed 0.4 m from the pivot on one side. Calculate the weight that must be placed 0.5 m from the pivot on the *other* side to balance the beam.
Answer:
Principle of Moments: Sum of clockwise moments = Sum of anticlockwise moments
(Force 1 x Distance 1) = (Force 2 x Distance 2)
(3.0 N x 0.4 m) = (Force 2 x 0.5 m)
1.2 Nm = Force 2 x 0.5 m
Force 2 = 1.2 Nm / 0.5 m
Force 2 = 2.4 N
Explanation: To balance, the clockwise moment created by the 3N weight must equal the anticlockwise moment created by the unknown weight.
A uniform beam is balanced on a pivot. A weight is placed on one side of the pivot. Explain why the beam is able to remain balanced using the principle of moments. Your explanation must include reference to both forces and distances.
Answer:
For the beam to be balanced, the total clockwise moment around the pivot must equal the total anticlockwise moment. A moment is the product of a force and the perpendicular distance from the pivot. Therefore, the force exerted by the weight multiplied by its distance from the pivot on one side must equal the force of another weight (or combination of weights) multiplied by *their* distance(s) from the pivot on the other side. If these values are equal, the beam will not rotate in either direction and remains balanced.
State the conditions necessary for an object to be in equilibrium.
For an object to be in equilibrium:
1. The resultant force acting on the object must be zero.
2. The resultant moment about any point must be zero.
Equilibrium means no net force and no net turning effect.
A 2N weight is placed 0.3m from a pivot. A force of 1.2N is applied on the other side of the pivot at a distance of 0.5m. Determine whether the object is in equilibrium, stating your reasoning.
Taking clockwise moments as positive, the clockwise moment = 2N * 0.3m = 0.6 Nm.
The anticlockwise moment = 1.2N * 0.5m = 0.6 Nm.
Since the clockwise and anticlockwise moments are equal (0.6Nm), the resultant moment is zero. Assuming that the resultant force in the system is zero, then the object is in equilibrium.
In reality, if there's a non-zero vertical force, there would be no equilibrium.
A 2.0 m long plank is pivoted at its center. A 30 N weight is placed 0.5 m from one end, and a 20 N weight is placed 0.3m from the other end. Calculate the additional force needed, applied at the opposite end to the 30N weight, to balance the plank.
The principle of moments states that for equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments.
Taking moments about the pivot:
Clockwise moment = (20 N * 0.7 m) = 14 Nm
Anticlockwise moment = (30 N * 0.5 m) = 15 Nm
Net anticlockwise moment = 15 Nm - 14 Nm = 1 Nm
To balance, additional clockwise moment needed = 1 Nm
Let the additional force be F.
F * 0.5 m = 1 Nm
F = 1 Nm / 0.5 m = 2 N
Answer: 2 N
A seesaw is balanced with two children on either side of the pivot. One child exerts a force of 300N at a distance of 1.2m from the pivot. The other child is sitting 1.0m from the pivot. Explain why the seesaw is balanced even though the forces exerted by the children are different.
The seesaw is balanced because the sum of the clockwise moment is equal to the sum of the anticlockwise moment. The moment is the turning effect of the force, which is calculated by multiplying the force by the perpendicular distance from the pivot. Therefore, even though the forces are different, if the product of force and distance are the same on both sides, the seesaw will be balanced. In this instance, the anticlockwise moment is 300N * 1.2m = 360 Nm. The force on the other side must be 360N to create a balancing clockwise moment of 360Nm (360N * 1.0m)
Describe an experiment, including necessary apparatus and method, to demonstrate that there is no resultant moment on a pivoted metre rule when it is in equilibrium. Two weights are to be suspended from the rule. Include details on how you would ensure accuracy.
Apparatus: Metre rule, pivot stand, two known weights (
State what measurements would be taken in an experiment to show that there is no resultant moment acting on an object in equilibrium when weights are hung on either side of a pivot.
The measurements that would be taken are:
1. The weight (force) of each hanging object, typically measured in Newtons (N).
2. The perpendicular distance from the pivot to the line of action of each weight, typically measured in meters (m).
Key Questions: Turning effect of forces
Define the moment of a force.
The moment of a force is a measure of its turning effect around a pivot. It is calculated as the force multiplied by the perpendicular distance from the line of action of the force to the pivot.
State the conditions necessary for an object to be in equilibrium.
For an object to be in equilibrium:
1. The resultant force acting on the object must be zero.
2. The resultant moment about any point must be zero.
Equilibrium means no net force and no net turning effect.
About Turning effect of forces (1.5.2)
These 12 flashcards cover everything you need to know about Turning effect of forces for your Cambridge IGCSE Physics (0625) exam. Each card is designed based on the official syllabus requirements.
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- 2 Definitions - Key terms and their precise meanings that examiners expect
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After mastering Turning effect of forces, explore these related topics:
- 1.5.1 Effects of forces - 24 flashcards
- 1.5.3 Centre of gravity - 6 flashcards
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