Forces Notes

Forces - Notes

pushes and pulls

Forces can

Weight - Gewichtskraft

Weight is the force acting on an object because of the gravitational pull from the centre of the Earth.

It can vary depending where you are on Earth. In Germany it is around $9.81 \frac{m}{s^2}$ or $9.81 \frac{N}{kg}$ (the units are equivalent).

Often, for sake of simplicity, $10 \frac{N}{kg}$ is used.

$$F = m \cdot g$$

(the formula will be explained later)

Planets with different masses will have different gravitational constants.

Hooke’s Law

Key question - How can we measure forces?

After, experimenting with different springs, Hooke discovered that up to a certain point (…), the springs expand proportional to a weight pulling the spring down.

extension of a spring is directly proportional to the force stretching the spring.

$$F = D \cdot l$$

directly proportional

the elastic constant of a spring is

$$D = \frac{F}{l}$$

P is called the elastic limit where the spring is permanently deformed.

You may see the formula as $D = \frac{F}{s}$ in a “Formelsammlung”.

newtons - the unit of force

the unit of force is called newtons (N), after Sir Isaac Newton

spring balance

force-meter - Kraftmesser

experiment 1

vectors to represent forces

vectors are a mathematical tool that is an arrow with

where is the forces acting upon the object - Angriffspunkt

direction - Richtung

size (magnitude) - Größe (magnus: Latin for “Great”)

addition of forces - Addition von Kräften

two small boats pulling a large vessel

subtraction of forces - Subtraktion von Kräften

Newton’s First Law of Motion

If the forces on a mass are balanced (no resultant force), then

balance of forces - Kräftegleichgewicht

While the friction of the block on the surface is so great (because of it’s weight) the forces are in balance. That means the block remains motionless. As the same force the man is pulling with is equal to the force of the force acting on the block. This is because of friction. (On a very smooth surface or with wheels the situation is different.)

friction - Reibung

what causes friction? -> surface structure

inclined plane - geneigte (schiefe) Ebene

geogebra app

The force due to the weight of the ball (die Gewichtskraft) is split into two components, one downhill (die Hangabtriebskraft) and one perpendicular to the surface (die Normalkraft).

Drag the point H to change the weight. Drag C to change the angle (inclination) of the plane.

TASK

Link to a Geogebra applet

erwünschte und unerwünschte Reibung

air resistance - Luftwiderstand

force and acceleration - Kraft und Beschleunigung

Newton

circular motion - Kreisbewegung


(c) 2019 sebastian.williams[at]sebinberlin.de - impressum und datenschutz - Powered by MathJax & XMin & HUGO & jsxgraph & mypaint