Force : Contact and Non Contact Force
BASIC SCIENCE JSS 2 THIRD TERM
Subject: BASIC SCIENCE
Class: JSS 2
Term: Third Term
Week: Week 5
Topic :
Force : Contact and Non Contact Force
Previous Knowledge: The pupils have previous knowledge of
that was taught in their previous lesson.
Behavioural Objectives : At the end of the lesson, learners will be able to
- Define force
- Mention types of forces
- Explain contact force and non contact force
- Say the effects of frictional force
Instructional Materials
- Wall charts
- Pictures
- Online Resource
- Textbooks
- Magnet
Methods of Teaching
- Role modelling
- Questions and Answers
- Explanation
- Discussion
- Recitation
- Imitation
- Story Telling
- Dramatization
Content:
Week 5
Topic: Force
Introduction
You must have seen a broken down vehicle in your town or village. Assuming this car is to be taken to a nearby mechanic village, what do you think must be done to it? To make the broken down car move to the mechanic village, you have to push it or get a towing van to pull it to the mechanic village. The pushing or pulling of the car to the place is an application of force. It is force that is pushing or pulling the car. To make the car go faster, we push harder, that is, we apply greater force. Note that push and pull are examples of force.
What is Force?
A force is a push or pull upon an object resulting from the object’s interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction.
In other words, force can be defined as a physical phenomenon that is capable of causing, increasing, retarding and changing the direction of motion and can stop motion.
Types of Forces
There are two types of forces, these are:
- Contact forces
- Non-contact forces
Contact Forces
A contact force exists between two or more surfaces when the force or source of the force is in contact with the object it is acting upon. For example, when people are pushing a car, they place their hands on the car and push.
Other examples include pull, frictional forces, reaction forces, tension forces and upthrust. More than one contact force can exist on a body. For example, a book placed on a table of weight W, is opposed by the reaction force R of the table. The pulling force F is counterpoised or counterbalanced by the frictional force acting between the table surface and the book.
Frictional force:- is a force that oppose the motion of one body over the other
.
Effect of frictional force
- It leads to wasting of energy, when two surrounding forces move over each other, heat is generated as a result of friction.
- The energy required to turn the machine, will be converted heat energy which reduces the energy output.
- It leads to wearing away of the surfaces in contact (wear and tear).
Non-contact Forces (Force Field)
We have explained that contact force exists between two or more surfaces. However, in a force field i.e. forces at a distance, it is not compulsory for the bodies in question to touch each other before a force can be experienced. Therefore, non-contact force or force field can be described as the region or space where force can be experienced. Examples of force fields include gravitational pull, magnetic and electric attraction and repulsion
Magnetic Force
What is a magnet? A magnet is a piece of metal that attracts iron or metallic objects. Magnetic force field is the space or region where magnetic force can be experienced. Magnetic force field can be produced in the surface around a bar magnet or in the region surrounding a current carrying conductor.
Magnetic force is the force that attracts metallic objects towards a magnet. If you bring two magnetic bars close to each other, you will experience any of these:
An attraction or a repulsion. If the two bars have the same pole (One end of a magnet is called pole and the two ends are called poles) repulsion occurs but, if they have different poles, then attraction occurs. This experience illustrates the discovery by Peter Peregrinus (i.e. like poles repel and unlike poles attract).
Gravitational force field
Gravitational force field course body thrown up to fall back on the ground. It is the force of the earth pull. This force makes anything that is thrown up to come back to earth.
Electric Force
You must have noticed that during harmattan, when you wear some clothing like those made from polyester, they produce some sound and in fact, some of them attract your body hair. This phenomenon can be explained as electric force. These are electric changes both in the clothing and in the body hair.
The Effects of Forces
A force acting on an object may cause the object to change shape, to start moving, to stop moving, to accelerate or decelerate. When two objects interact with each other they exert a force on each other, the forces are equal in size but opposite in direction.
- Force is an influence tending to change the motion of a body or produce motion or stress in a stationary body.
- Force change the motion of a body: Force changes the motion of body that are already in motion and produce motion in a stationary body. Example a car moving on a road suddenly hit behind by a truck, you will notice the tendency of the car motion increase. The force applied by the truck affect the motion of the car. A stationary body hit behind by a moving body, the position of the stationary body changes.
- Force change the direction of both stationary body and body in motion: Newton second law state that the rate of change of momentum of a body is directly proportional to the applied force and take place in the direction in which the force acts.
Presentation:
The topic is presented step by step
Step 1: The class teacher revises the old topic
Step 2: The class teacher introduces the new topic
Step 3: The class teacher allows the pupils to give their own contributions and gives room for pupils” participation
Class Teacher and Pupils Activities. Interaction or Participation
This involves class teacher and pupils’ interaction, conversation, imitation or modeling through discussion, play method or just by recitation or asking and answering questions that are related to the topic that has just been taught
- The class teacher asks the pupils to point the north and south poles of the magnet to each other and say what they observe.
- The pupils are shown the differences between a pull or a push.
- Pupils are encouraged to say what they have been taught about the early forces
Evaluation
- A force can either be a ________________ or a ________________
- Explain the difference between pulling and pushing
- What is a magnet?
- What is gravity?
- Define Force?
- Mention 2 types of force
- Is gravity a pull force or a push force
- Write out 4 objects that can be picked up by a magnet
- Write out 4 objects that cannot be picked up by a piece of magnet
- The south and north poles of the magnet ________________ each other (repels, attracts)
Conclusion
The class teacher goes round to mark and he or she does the necessary corrections
