Lesson 12 Chapter 4

Force and motion
1 / 23
next
Slide 1: Slide
PhysicsMiddelbare schoolvwoLeerjaar 3

This lesson contains 23 slides, with text slides and 2 videos.

time-iconLesson duration is: 45 min

Items in this lesson

Force and motion

Slide 1 - Slide

This lesson
  • Recap
  • free fall
  • acceleration due to gravity
  • studying

Slide 2 - Slide

Newtons First law of motion

Newtons second law of motion

Slide 3 - Slide

Newtons first law — Inertia





Newtons second law

Slide 4 - Slide

Newtons first law — Inertia
  • An object at rest remains at rest, and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force.


Newtons second law

Slide 5 - Slide

Newtons first law — Inertia
  • An object at rest remains at rest, and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force.


Newtons second law
Fres=ma

Slide 6 - Slide

Newtons first law — Inertia
  • An object at rest remains at rest, and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force.


Newtons second law
Fres=ma
[1N]=[1kg][s2m]

Slide 7 - Slide

Inertia
The property of mass that it resists changing speed

Slide 8 - Slide

Free Fall
  • Acceleration due to gravity 

Slide 9 - Slide

Slide 10 - Video

Slide 11 - Slide

Falling in the air
A v-t diagram of a skydiver jumping out of a plane

Slide 12 - Slide

Slide 13 - Video

4.3 Force and work

Slide 14 - Slide

work
  • Forces cause objects to accelerate (change speed).

  • Changing in speed means an object gains or looses kinetic energy (movement energy)

  • Work is a measure of how much kinetic energy a force transfers to an object.

Slide 15 - Slide

Work
  • W: the work that the force has carried out (the amount of kinetic energy a force has transferred to an object).
  • F: The magnitude of the force acting out the work.
  • S: The distance this work caused the object to move.
W=Fs

Slide 16 - Slide

Work
  • W: the work that the force has carried out (the amount of kinetic energy a force has transferred to an object).
  • F: The magnitude of the force acting out the work.
  • S: The distance this work caused the object to move.
W=Fs
A force that causes an object to move is called a motive force

Slide 17 - Slide

Work
W=Fs
Quantity
Unit
Work (W)
Newton-meter (Nm)
Force (F)
Newton
Distance covered (s)
meter

Slide 18 - Slide

Practice problem
Jane and Wendy are going on holiday. They attach their caravan to the car and drive to the campsite, 50 km away (figure 2). The car exerts a pulling force of 1.2 kN on the caravan.
Calculate the work done on the caravan.

Slide 19 - Slide

Work and energy
  • work is related to energy. 

  • 1 Newton-meter of work = 1 joule of energy

  • When considering for example a carengine, the work done by the car comes from the useful energy supplied by the engine.

Slide 20 - Slide

Work and energy
η=EtotEused100
Eused=work

Slide 21 - Slide

Practice problem
Dimah uses the setup in figure 4 to determine the efficiency of a small electric motor. The motor takes 6.0 s to pull the wood block 1.8 m. During those 6.0 s, the voltmeter reads 1.5 V and the ammeter 0.64 A. The tractive force acting on the wood block is 2.5 N.

P=UI
η=EtotEused100
W=Fs

Slide 22 - Slide

Practice exercises – 4.3
  • Exercise 5
  • Exercsise 7
  • Exercise 8

Slide 23 - Slide