Recognising ForcesRecognising Forces

D. Crowley, 2007

Recognising ForcesRecognising ForcesTo know, and be able to recognise the different types of force

Wednesday, April 19, 2023

How?How? Have a look at the picture of the toy shark (made of

plastic)- how is it suspended in the air?

Discuss this with your partner…

Have a look at the picture of the toy shark (made of plastic)- how is it suspended in the air?

Discuss this with your partner…

ForcesForces The toy shark is being held in place by a specific force

This force is known as magnetism, and works by the two poles repelling each other: -

The toy shark is being held in place by a specific force

This force is known as magnetism, and works by the two poles repelling each other: -

Magnet

Magnet

N S

N S

ForcesForcesWhat is force?What is force?

A force is a push or a pull upon an object

There are two categories of force. These are: -There are two categories of force. These are: -

Contact forces - two objects in contact with each otherNon-contact forces - a force that acts over a distance

Gravity - non-contact forceFriction (via brake discs) - contact force

Types of ForceTypes of ForceWhat types of force are there?What types of force are there?

Gravitational Force - acting straight downwardsMagnetic Force - push / pull exerted by a magnetElectrical Force - a force between two charged objects

Reaction Force - force from the surface, usually acting straight upwardsContact Force (push / pull forces) - force which results in the object speeding up, for example, due to an engine / rocketFriction - friction between surfaces slowing an object down. This can include air resistance - (special type of frictional force) where air in the atmosphere slows down a moving objectTension Force - pulling of a rope / cable from opposite ends Elastic Force - compression / extension of a spring or elastic product

Represent a ForceRepresent a ForceHow can we represent force?How can we represent force?

We represent forces using arrows - the arrow points the way the force is working

The arrow also represents the size of the force - the bigger the arrow, the greater the force is. These arrows always come in pairs…

Gravity

Reaction

For example, when an apple is sitting on a desk there are two forces affecting it - gravity trying to pull it down, and the reaction force of the desk, pushing it back up

If these forces balance, then the apple remains at a steady speed. The horizontal forces are also equal and opposite, else the object would accelerate sideways (and fall off)!

Represent a ForceRepresent a ForceHow can we represent force?How can we represent force?

When we draw a force, we need to include all the arrows that affect our object. These arrows always work in pairs - if there is a force one way, there will be an opposite force the other way.

The bigger the arrow, the bigger the force.

Look at the following, and see if you can decide where the force arrows should be…

Apple, on a desk Stationary car Space shuttle, accelerating upwards

Represent a ForceRepresent a ForceForces circusForces circus

You know have a chance to look at various forces for yourself. Try and identify what force is being demonstrated at each area, and answer the questions on the worksheet.

You need to work in pairs, with no more than 3 pairs at each work area. You will have just three minutes at each area, so be quick!

Remember, contact forces (two objects in contact with each other) and non-contact forces (acting over a distance).Gravitational Force; Magnetic Force; Electrical Force; Reaction Force; Contact Force (push / pull forces); Friction (air resistance); Tension Force; Elastic Force

StationsStationsStation 1Station 1

Elastic force - contact forces

Station 2Station 2

Gravitational and reaction forces - contact forces

Station 3Station 3

Magnetic force; frictional force; gravitational and reaction - non-contact and contact forces

Station 4Station 4

Electrical force - non-contact forces

StationsStationsStation 5Station 5

Gravitational; reaction; friction; contact forces - contact and non-contact forces - fell at different speeds due to different frictional forces

Station 6Station 6

Gravitational and frictional forces (air resistance) - contact and non-contact forces - fell at different speeds due to different frictional forces (air resistance)