# Aim: How can we describe resultant force (net force)?

## Presentation on theme: "Aim: How can we describe resultant force (net force)?"— Presentation transcript:

Aim: How can we describe resultant force (net force)?
Identify some forces. Identify the unit for force. Explain the difference between mass and weight. A student has a mass of 75 kg. The student weighs 831 newtons. Determine the acceleration due to gravity.

Aim: How can we describe resultant force (net force)?
List all vectors and units.

How can we describe forces acting on an object?
Two or more forces that act on the same object at the same time are called concurrent forces. Ex:

Combining forces Resultant force (net force)
Is the single force that is equivalent to the combined effect of these concurrent forces. Example 1: F1=10N F2=5N R = 15N Feq= -15N

The force vector needed to produce equilibrium is the same length as the resultant vector but it is pointing in the opposite direction. (Feq)

Example: 3 If forces act in opposite directions, the angle between them is 180 degrees, the resultant force is the smallest. F2 = 10N F1 = 3N F1 = 3N F2 = 10N

Combining forces Head-to-tail method – combine the head of one vector to the tail of the other vector. If two forces act in the same direction, the angle between them is 0 degrees and the resultant force is the sum of their magnitudes (R = F1+F2) Ex2: F1=10N F2=3N F1=10N F2=3N R = 13N

Sketch the Resultant force and Equilibrium force

How can we sketch the equilibrium force?
The vector sum of the concurrent forces acting on an object is called the net force Fnet. (Resultant force) If the net force acting on the object is zero, the object is in equilibrium. F2 F1 F1 R Feq F2

If two concurrent forces act at right angles to each other, the head-to-tail method produces a right triangle. F2 R F2 F1 F1

When is resultant force is greater?
When the two forces act in the same direction, 0 degree angle, they produce the largest resultant force. When the two forces act in opposite directions, 180 degree angle, they produce the smallest resultant force.

How can we analyze force vectors?
Find the resultant force vector. A 10 Newton force and a 4 Newton force act concurrently on a point. As the angle increases from 0° to 180° what happens to the resultant force? 3N 7N

Triangular method of adding concurrent forces.
Leave the first force in the same position. Take the second force and slide it to the head of the first force. (Head-to-tail method) To find the resultant force: draw a line from the tail of the first force vector to the head of the last vector. To find the equilibrium force: draw the same size line as the resultant force but 180° from the resultant force. F2 F1 F1 R F2

Draw the resultant force for the following vectors.
Examples Draw the resultant force for the following vectors. F2 R F1 F1 F2 P P

Examples F2 F1 F3 F1 F2 R F3

Equilibrium force The vector sum of the concurrent forces acting on an object is called the net force Fnet. (Resultant force) If the net force acting on the object is zero, the object is in equilibrium. The force vector needed to produce equilibrium is the same length as the resultant vector but it is pointing in the opposite direction. (Feq) F2 F1 F1 R Feq F2

If two concurrent forces act at right angles to each other, the head-to-tail method produces a right triangle. F2 R F2 F1 F1

Let’s calculate the resultant force vector using Pythagorean theorem
c2 = a2 + b2 Use physics terms: R F2 = 40N F1= 30N

Using Soh Cah Toa, find angle theta. (hint: Toa)
Using the same example in the previous slide. What is the angle of the resultant force. (The angle is located next to the tail of the resultant force) Using Soh Cah Toa, find angle theta. (hint: Toa) R = 50N F2 = 40N θ F1= 30N

Aim: How can we analyze force vectors and components?
Calculate the resultant force and the angle. Sketch and label the equilibrium force. 10N 5N

Example: Find the resultant force and the angle.
R = 11.1N R = ? F2 = 10N θ F1= 5N

Aim: How can we analyze force vectors?
Sketch the resultant force and equilibrium force. Calculate the magnitude of the equilibrium force. 2N 7N

1) Which pair of vectors produce the greatest resultant force?
2) Which pair of vectors produce the least resultant force?

Where should we draw vector B?
The diagram below represents a force vector A, and resultant vector, R. Where should we draw vector B? Recall: The resultant vector goes from start to end. B R A

Where should we draw vector B?
The diagram below represents a force vector A, and resultant vector, R. Where should we draw vector B? B R A

Force vector components
A person is pulling a sled with a 100-newton force at a 30° angle with the horizontal. 1) Sketch a picture 2) Calculate the horizontal force. 3) Calculate the vertical force. 4) As the angle decreases, describe the horizontal force and vertical force.