Effects of Forces

Effects of forces
● Know that forces may produce changes in the size and shape of an object
● Length of the body before applying the stretching force/load/weight is called
unstretched length.
● Length of the body after applying the stretching force/load/weight is called
stretched length.
● Difference between the stretched length and the unstretched length of the body is called
extension.
Extension = stretched length - unstretched length
Hooke’s Law :
● Within limit of proportionality, the extension of a spring is directly proportional
to the load applied on it.
F = kx
𝐹
k= 𝑥
● Where:
○ F is the force applied
○ k is the spring constant
○ x is the extension of the spring
● The spring constant is the force per unit extension
○ The units are N/mm or N/cm or N/m
○ The spring constant is a measure of how stiff the spring is
● The point beyond which Hooke’s law is not obeyed is called limit of proportionality.
Calculation of Spring constant from the graph :

𝑦 −𝑦 𝑥2 − 𝑥1
k = gradient of the line = 2 1
𝑥2 − 𝑥1
k = gradient of the line = 𝑦2 − 𝑦1
Effects of forces
● Know that an object either remains at rest or continues in a straight line at constant speed unless
acted on by a resultant force.
● A resultant force may change the velocity of an object by changing its direction of motion or its
speed.
● Resultant force equation : F = ma S.I. unit = Newton (N)
● know that the force and the acceleration are in the same direction.
Friction :
Solid friction is the force between two surfaces that may impede motion and produce heating
Know that friction (drag) acts on an object moving through a liquid
Know that friction (drag) acts on an object moving through a gas (e.g. air resistance)
Effects of forces
Circular motion :
Speed of an object not changing.

Velocity of an object changing due to change in direction
Object is accelerating then,according to F = ma
There is resultant force acting on an object towards the centre of circular path ( centripetal force )
Acceleration is also directed towards centre of circular path.
Resultant force acts perpendicular to the motion of an object.
2
𝑚𝑣
F= 𝑟
(a) speed increases if force increases, with mass and radius constant
(b) radius decreases if force increases, with mass and speed constant
(c) an increased mass requires an increased force to keep speed and radius constant
Turning effect of forces :

The turning effect of a force is called the moment of the force.
Moment of a force = force x perpendicular distance from pivot.

M=Fxd
The S.I. unit of moment of force is Nm.

Pivot : the point about which the object rotates is called as the pivot.
How to increase the turning effect of force ?
➔ By increasing force
➔ By increasing perpendicular distance from the fixed point ( pivot )
Examples of Moment of a force :
1.The most popular examples of the moment of force in real life are the opening and closing of a door
along a fixed hinge. When force is applied to a door, the hinge acts as a pivot. The generated moment of
a force turns the door.
2. Another example of moment of a force is unscrewing a nut with a spanner. A spanner adds
distance between the nut and the force, allowing for a moment to be created that unscrews the nut.
Effects of forces
Conditions for equilibrium :

1. The sum of forces in one direction is equal to the sum of forces in the opposite direction.
( Resultant force on a body is zero )
2. The sum of anticlockwise moments about any point is equal to the sum of clockwise moments about the same
point. ( Resultant moment on a body is zero )
This condition is also known as principle of moments.
Total anticlockwise moment = Total clockwise moment
Describe an experiment to demonstrate that there is no resultant moment on an object in

equilibrium
- Suspend a metre rule horizontally from its centre (O) using a strong thread
- Suspend two differing masses (W1 and W2) on either side of the thread
- Adjust the distances of two weights until the ruler is balanced and horizontal
- Calculate the weight of each mass
- Using the equation W = mg
- Calculate the clockwise and anti-clockwise moment
- Using the equation: moment = force x perpendicular distance from pivot
- Clockwise moment = W2 × L2
- Anti-clockwise moment = W1 × L1
- If the ruler is horizontal (in equilibrium), clockwise moment = anti-clockwise moment
Effects of forces
Effects of forces

Effects of Forces

Uploaded by

Copyright:

Available Formats

Effects of Forces

Uploaded by

Document Information

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Effects of Forces

Uploaded by

Copyright:

Available Formats

Effects of forces

Calculation of Spring constant from the graph :

Speed of an object not changing.

Turning effect of forces :

Moment of a force = force x perpendicular distance from pivot.

The S.I. unit of moment of force is Nm.

Conditions for equilibrium :

Total anticlockwise moment = Total clockwise moment

Describe an experiment to demonstrate that there is no resultant moment on an object in

You might also like