Topic: We move heavy objects

Supplementary material for use in lessons in the group of natural sciences (nature, biology, chemistry, geography, physics), additional classes, science clubs. It can serve as a resource for expanding knowledge, preparing students for science competitions.

Target group:

7th‑grade students of elementary school (physics).

Core curriculum

7th‑grande of elementary school – physics

II. Movement and forces. Student:

11 ) recognizes and names forces, gives examples in various practical situations (strength: heaviness, pressure, resilience, resistance to movement).

General aim of education

The students will experimentally examine the friction and air resistance forces and give examples of reducing and increasing friction and resistance.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• explain what friction is and what resistance is;

• enumerate examples of the use of friction in everyday life;

• indicate ways to increase or decrease the friction force depending on your needs;

• enumerate animals that reduce the friction force to move more efficiently.

Methods/techniques

• activating

  • discussion.

• expository

  • talk.

• exposing

  • film.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in pairs;

• activity in groups;

• collective activity.

Teaching aids

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers;

• shoe with a smooth sole;

• shoe with a clearly retreaded sole.

Lesson plan overview

Before classes

• Students get acquainted with the content of the abstract. They prepare to work on the lesson in such a way to be able to summarize the material read in their own words and solve the tasks themselves.

Introduction

• The teacher explains the aim of the lesson and together with students determines the success criteria to be achieved.

Realization

• Students read the fragment Fri „Nuisance friction” and write the definition of friction in the notebooks.

• The teacher announces a movie. He instructs his pupils to write a research question and a hypothesis in the form provided in the abstract. Then he plays the video and the students note their observations and conclusions. The teacher points the person who shares his insights and explains the reasonableness of the conclusions noted.

• The teacher asks the pupils how to reduce or increase the friction force - the students' ideas are written on the board. Students read the fragment Fri „Increase and decrease friction” and give ways that have not yet been included on the board.

• The teacher shows students the soles of shoes that clearly differ in retreading. He asks which shoe ensures safe movement on the slippery surface and asks for justification of the answer.

• The teacher instructs students to independently perform an interactive exercise consisting in indicating examples of useful friction and examples of harmful friction. Together with students, he discusses correct solutions.

• Students will get acquainted with the fragment „Resistance” and perform an interactive exercise: mark the illustrations on which animals with a streamlined body shape are shown.

Summary

• At the end of the class, the teacher asks the students questions:

  • What did you find important and interesting in class?

  • What was easy and what was difficult?

  • How can you use the knowledge and skills you have gained today?

  Willing/selected students summarize the lesson.

Homework

• Listen to the abstract recording at home. Pay attention to pronunciation, accent and intonation. Learn to pronounce the words learned during the lesson.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

We move heavy objects

If you happened to have seen how adults move heavy furniture, e.g. a cabinet, you know that it’s not an easy task. First you should take all items out of the piece of furniture you wish to move. This will reduce its mass and weight. What good will that do? In order to move a piece of furniture you have to overcome the force with which it presses against the floor. When trying to move one surface over another, you always meet certain resistance. That is the friction that we have to overcome. It occurs always where two surfaces that we wish to move in relation to each other meet.

Factors affecting the force of friction are:

• pressure force – the greater the pressure force exerted by one body (i.e. any object) on another, the greater the friction force present where they come into contact, that’s why lighter objects are easier to move;

• type of surface of objects that come into contact – the rougher and more uneven the surfaces that come into contact, the harder it is to move them.

If you want to move any objects, in particular heavy ones, you need to reduce friction. During friction individual particles are detached from the substance, which may lead to the complete destruction of objects or mechanisms. That’s why sometimes it’s necessary to reduce friction. Substances most commonly used for this purpose are greases and oils – e.g. in car engines. Motor oil protects moving engine components against destruction, allowing them to operate for a longer time. Sometimes it’s possible to use various materials that exhibit less friction against the floor, e.g. a blanket or towel – this also allows to move objects more easily.

Friction can also be reduced by rolling an object instead of moving it. Another method to reduce friction force is to reduce the mass of objects, i.e. the pressure force exerted on the surface. You can also try to smoothen surfaces that come into contact with each other as much as possible, for example by polishing them.

Sometimes it’s necessary to achieve better stability and grip, e.g. in the case of car tires. In such case, friction must be increased. It can be achieved by forming grooves on the surface. Friction also makes it possible to break safely.

Friction is connected with drag forces. These are all the forces that we must overcome when we want objects to be move.

The greater the density of medium surrounding the body, the greater the resistance. That’s why it’s easier to move in the air. The object’s shape is also of great importance. It’s said that the shape is aerodynamic when it enables improved flow of medium particles around the object.

Aerodynamic shapes are very common in the animal world: they enable fish to swim fast and birds to fly. By watching animals, humans also began constructing vehicles in a way that allows them to experience the least drag. Aircraft and their hulls are modelled based on the silhouettes of birds, whereas the shape of submarine hulls evokes fish. However, not only vehicles that move through the air or water must have the most aerodynamic shape. Giving an aerodynamic shape to a motor vehicle allows to reduce drag, which affects fuel consumption. Nevertheless, there are situtations where increasing drag forces can also be useful.

Using a device known as the double‑ended lever, it’s possible to move large objects. The longer the lever arm on which pressure is exerted and the shorter the arm on which the object being lifted rests, the less force is required to lift it.

In order to transport a heavy object to a higher storey, it’s not necessary to lift it directly off the ground. Instead, it’s possible to use a pully or a system of pulleys. This will allow to pull the heavy object high up.

• Friction is a force created when two surfaces that come into contact move against each other.

• Drag is created when moving an object through a medium, e.g. water and air.

• Fiction and drag can be increased or reduced as needed.

• A double‑sided lever and pulleys are simple machines that allow to perform the same work using less force.