Force
- A force is push or pull exerted on an object.
- Force is a vector quantity that has magnitude and direction.
- The unit of force is Newton ( or kgms-2).
Unbalanced Force/ Resultant Force
When the forces acting on an object are not balanced, there must be a net force acting on it. The net force is known as the unbalanced force or the resultant force.When a force acts on an object, the effect can change the
- size,
- shape,
- stationary state,
- speed and
- direction of the object.
Newton's Second Law
The rate of change of momentum of a body is directly proportional to the resultant force acting on the body and is in the same direction.Implication:
When there is resultant force acting on an object, the object will accelerate (moving faster, moving slower or change direction).
Formula of Force
![](http://www.one-school.net/Malaysia/UniversityandCollege/SPM/revisioncard/physics/forceandmotion/images/forceformula.png)
From Newton's Second Law, we can derived the equation
(IMPORTANT: F Must be the net force)
Summary of Newton's 1st Law and 2nd Law
Newton's First Law:
When there is no net force acting on an object, the object is either stationary or move with constant speed in a straight line.
Newton's Second Law:
When there is a net force acting on an object, the object will accelerate.
Newton's First Law:
When there is no net force acting on an object, the object is either stationary or move with constant speed in a straight line.
Newton's Second Law:
When there is a net force acting on an object, the object will accelerate.
Example:
A box of mass 150kg is placed on a horizontal floor with a smooth surface; find the acceleration of the box when a 300N force is acting on the box horizontally.
Answer:
F = ma
(300) = (150)a
a = 2 ms-2
A box of mass 150kg is placed on a horizontal floor with a smooth surface; find the acceleration of the box when a 300N force is acting on the box horizontally.
Answer:
F = ma
(300) = (150)a
a = 2 ms-2
Example:
A object of mass 50kg is placed on a horizontal floor with a smooth surface. If the velocity of the object changes from stationary to 25.0 m/s in 5 seconds when is acted by a force, find the magnitude of the force that is acting?
Answer:
We know that we can find the magnitude of a force by using the formula F = ma. The mass m is already given in the question, but the acceleration is not give directly.
We can determine the acceleration from the formula
From the formula
F = ma = (50)(5) = 250N
The force acting on the box is 250N.
A object of mass 50kg is placed on a horizontal floor with a smooth surface. If the velocity of the object changes from stationary to 25.0 m/s in 5 seconds when is acted by a force, find the magnitude of the force that is acting?
Answer:
We know that we can find the magnitude of a force by using the formula F = ma. The mass m is already given in the question, but the acceleration is not give directly.
We can determine the acceleration from the formula
From the formula
F = ma = (50)(5) = 250N
The force acting on the box is 250N.