5-2 Resultant force (5.2)

Lesson goals:

Understand what a driving force is and

what a resisting force is.

Make calculations with a resultant force.

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Slide 1: Slide

NatuurkundeMiddelbare schoolhavoLeerjaar 3

This lesson contains 18 slides, with interactive quiz, text slides and 3 videos.

Lesson duration is: 45 min

Items in this lesson

Lesson goals:

Understand what a driving force is and

what a resisting force is.

Make calculations with a resultant force.

Slide 1 - Slide

Resultant force (5.2)

Slide 2 - Slide

Driving force and resisting force

The two most important resisting forces:

- Air friction

- Rolling friction

and driving forces are

- gravity

- force of a motor

- pushing force

Slide 3 - Slide

Air friction

Air friction is due to the collision with

air particles

You can decrease air friction by:

- improving your streamline

- making your frontal cross-section

smaller

Slide 4 - Slide

Forces on a car...

= pushing foce

= frictional force

The pushin force and frictional force act in the opposite directions. is greater than

therefore

is to the right.

F^{​ p ​ ​}

F^{​ r ​ ​}

F p

F^{​ r ​ ​}

F^{​ r e s ​ ​}

Slide 5 - Slide

Resultant force causes acceleration

If the pushing force is equal to the frictional force then the resultant force is equal to 0 N

Then there is no acceleration THEREFORE

the car stand still OR
the car has a constant velocity

F^{​ p ​ ​} = F^{​ r ​ ​}

F^{​ r e s ​ ​} = 0 N

Slide 6 - Slide

Resultant force changes velocity

If the pushing force is greater than the frictional force the resultant force is greater than 0 N

The acceleration will be in the

direction of the resultant force.

This is also known as Newtons

first law of motion

F^{​ p ​ ​}

F^{​ r ​ ​}

Slide 7 - Slide

Resultant force changes velocity

If there is no pushing force only the frictional force is left and the resultant force acts opposite

to the the direction of motion.

The car will decelerate

(or rather have a negative

acceleration)

Slide 8 - Slide

Example

Slide 9 - Slide

Slide 10 - Slide

Slide 11 - Slide

Slide 12 - Slide

The resultant force can do three things

Accelerate an object (if the resultant force is in the direction fo motion),
Decelerate an object (if the resultant force is in the opposite direction of motion)
Change direction of an object

(when a force comes from the side)

Slide 13 - Slide

Slide 14 - Video

Slide 15 - Video

Slide 16 - Video

Now try the following question in your digital method.

17, 18 and 19

Slide 17 - Slide

How did the lesson go? Any questions?

Slide 18 - Open question