Effects of Force

Card 1: Newton's Second Law

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).

Card 2: Force

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).
Card 3: Formula of Force

Formula of Force

From Newton's Second Law, we can derived the equation (IMPORTANT: F Must be the net force)

Card 4: Summary of Newton's 1st Law and 2nd Law

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.

Example 1
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.

F = ma
(300) = (150)a
a = 2 ms-2

Example 2
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?

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

\begin{gathered}
a = \frac{{v - u}}
{t} \hfill \\
a = \frac{{25 - 0}}
{5} = 5ms^{ - 2}  \hfill \\
\end{gathered}

From the formula
F = ma = (50)(5) = 250N

The force acting on the box is 250N.

Card 5: Effects of Force

Effects of Force

When a force acts on an object, the effect can change the

• size,
• shape,
• stationary state,
• speed and
• direction of the object.
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