Forces

Forces

Multiple Choice

Is force a scalar or vector quantity?

• Scalar

• Vector

Multiple Choice

What is the unit of Force?

• Watt (W)

• Ampere (A)

• Newton (N)

• Volt (V)

What is a force?

A force is simply a push or pull.

Forces have both size and direction.

Net Force

A net force is the resultant force as a result of two or more combined forces.

Some Tips For Calculating Net Forces

• Forces in the same direction ADD.

• Forces in opposite directions SUBTRACT

Multiple Choice

What is the net force produced by the two forces acting on the wagon in the picture?

• 30N

• 50N

• 10N

Multiple Choice

What is the net force on the wagon shown in the picture?

• 60 N

• 40 N

• 20 N

• 10N

Multiple Choice

What net force is acting on the wagon in the picture?

• 50N

• 25 N

• 0 N

• 20N

Balanced and Unbalanced Forces

• Balanced: When the net force on an object is equal to zero. This hence does not cause any change in motion.

• Unbalanced: When the net force on an object is not equal to zero. This therefore causes change in motion.

Multiple Choice

Which of the following experiences a BALANCED force?

• a

• b

• c

Multiple Select

Which of the following experiences an UNBALANCED force?

• a

• b

• c

What is Motion?

When an object changes position with time with respect to a reference point, we say that the object is in MOTION.

Speed

Speed is defined as the rate of change of distance with time.

The formula for speed is

 $Speed\ =\ \frac{Dis\tan ce\ travelled\ }{Time\ taken}$  

Let's work on these questions

1) 5 m/s

2) 0.002 km/s or 2 m/s

3) 10 s

4) 1000 m

5) 500 s

Velocity

Velocity is defined as the displacement of an object per unit time.

It is basically speed in a direction

 $Velocity\ =\ \frac{Displacement}{Time}$  

Let's look at these questions

1) 30 m

2) by changing direction, by changing covering the same distance in less time or by covering less distance in the same time.

3) No, because the direction is constantly changing and hence velocity is changing.

4) No, they are not going in the same direction.

Acceleration

Acceleration is defined as the rate of change of velocity with time.

 $acceleration\ =\ \frac{change\ in\ velocity}{time}$  

 $acceleration\ =\ \frac{final\ velocity\ -\ initial\ velocity}{time}$  

Let's look at this question

Answer: 5 m/s²

Video

Let us look at the video below to understand Newton's Laws of motion further

https://www.youtube.com/watch?v=mn34mnnDnKU

Newton's Law of inertia

• Mass (m) is the measure of amount of matter in an object.

• Inertia is the property of an object which describes how much it will resist change in motion of the object.

• The greater the mass of an object, the greater the inertia.

What is this unbalanced, opposing force to motion?

FRICTION!!!!!!!

There are four types of Friction.

• Sliding friction- ice skating

• Rolling friction- bowling

• Fluid friction (air or liquids) - air resistance

• Static friction- initial friction when moving an object at rest.

This song will help you remember

https://www.youtube.com/watch?v=OaKc4PlrEY8

This song will help you remember Newton's second law of motion

https://www.youtube.com/watch?v=tZ-rp5YmRkQ

This final song will help you remember ALL of Newton's laws of motion

https://www.youtube.com/watch?v=PkAO8F-Tm-w

Let's now test what we have learnt in the lesson

Open Ended

What does Newton's First law state?

Multiple Choice

Does Newton second law state that force is proportional to acceleration?

• Yes

• No

Multiple Choice

Does inertia depend on the mass of a person?

• Yes

• No

Poll

Rate how well you understood forces.

• 100% understood everything

• mostly understood

• did not understand

• need time to understand