What Is A Force (KS2)
In primary school KS2 Science, kids start to get to grips with what forces are. Whether you’re helping with homework, or just want to understand what your child is talking about, let Kidadl help you understand.
When standing still, a force can either keep you from moving or help you start moving. When you’re already moving, a force can help you speed up or slow down. We need forces to move! Read on to find out all about forces and how they govern everything around us.
What Is A Force In Science?
A force is, most simply, a push or pull in a certain direction. We use our energy to apply forces to things (like lifting ourselves out of bed) and we use machines to apply forces for us (like pulleys, wheels, screws and gears which can lift very heavy objects). A pulley is what we call a simple machine. This is because it will take a small force and turn it into a bigger one. When the force becomes bigger, we can do more with it, and we can even do things faster.
Image © Georg Eiermann
What Are The Five Forces In Science?
Primary School children need to know about forces acting in five different ways: gravity, the magnetic force and three frictional forces (air resistance, water resistance and surface resistance).
Gravity is a force from the Earth that pulls. It’s the Earth doing the pulling, and everything in the universe that’s being pulled. The Earth draws things from its centre, like a magnet. So, gravity from the Earth is what pulls us down when we go up! Gravity also holds the solar system in place, helping the planets and moons to keep the right distance as they move around each other, and the Sun. Gravity is also what causes us to have weight.
The closer the object is to the Earth, the stronger the pull you feel. Which is why when we jump up, the Earth pulls us down, because we’re close enough to draw in. If we were a hundred light-years away instead (which is very far), the Earth’s centre would have a long way to reach, and after all of that stretching to reach us, it would be so weak that there wouldn’t be much strength to draw us back.
Image © Mylene2401
2. Magnetic Force
Magnetic force can also be a push or pull. It is what pulls the north pole and south pole on magnets together. It’s also what pushes two north poles apart and pushes two south poles apart. It’s the reason why certain metallic things seem to ‘stick’ together. Magnetic force plays an important role in electricity too.
Image © Jason Leung
The Frictional Forces
The following three frictional forces all have resistance in their names because they mostly act to resist motion and slow you down, or stop you from moving completely.
Friction can be a push or a pull and kind of sticks things together. Depending on how much friction there is between two objects, they could stick, rub, slip or slide. For example, water on hard floors reduces friction between us and the floor, which is why it becomes slippery to us.
3. Surface Resistance
Surface resistance is a type of force that acts between two surfaces: for example, the surface of your plate and the surface of your table. The higher the surface resistance, the less slipping and sliding there will be. If your table has a rough texture, the plate will barely slide on the table, because the surface resistance is so high.
If you have a super smooth, polished table, and a very smooth plate, there will be lots of sliding because the surface resistance is low. A good amount of surface resistance is helpful for keeping us safe, for example on roads while driving. When surfaces are too smooth, it can be dangerous.
Image © Aaron Barnaby
4. Air Resistance
Air resistance is a force that acts against things moving in the air. When something or someone is moving up in the air, it tries to drive them down. If they’re moving down, it tries to push them up. If they’re moving to the left, it will try to move them to the right. If they’re moving to the right, it will try to move them to the left. Air resistance helps parachutes land safely, by slowing them down in the air!
Bonus Fact: Smoother objects feel less resistance when they move in the air.
Water resistance is like air resistance, except that instead of acting on things moving in the air, it acts on things moving in the water. This includes things floating on the water too. This is why in swimming lessons kids are told to keep their fingers together and pointed- this is so that there is less force and they can swim faster.
Teaching Forces In Primary School
KS1 children (Year 1 and Year 2) will come to understand the difference between a push and a pull.
Teaching about forces and motion for KS2 children begins in Year Three.
In Year 3: kids explore how different objects interact with different surfaces, as well as beginning to learn about the behaviour of magnets.
In Year 4: Knowledge gained in Year Three is drawn upon, and a greater understanding is developed.
In Year 5: Children are introduced to gravity, air resistance and water resistance, as well as how frictional forces can slow or stop motion. They will also learn about simple machines, how they can make smaller forces larger, to apply on objects and cause large impacts.
In Year 6: Knowledge gained in Years 3 to 5 are drawn upon, with a greater understanding developed.
Primary School children may learn this through a range of experiments, such as:
Investigating Surface Friction: How cars roll across the carpet, versus how they roll across the hard floor.
Investigating Air Resistance: Which shape of paper plane travels fastest in the air.
-Fill a sink with water, and take turns placing different objects in it. Floating or sinking, this is a great way to identify the force resisting the motion. To make this activity even more special, why not try experimenting with an Aluminium Foil boat?
-Observe how a balloon fights forces as it moves through the air, compared to a soft ball. Try throwing both up, observing how quickly each lands.
-Explore how quickly a toy car moves across the carpet, compared to a table with water on.
-Make a paper parachute for a toy, then explore how well it slows the motion of the toy. Then, invent a new parachute that works better than the first one.
-Take a number of small objects and drop them from the same height, one at a time. Which falls fastest and why?
Curious to find out what else your child knows about? Take a look at our helpful science trivia questions by key stage.
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KS2 Forces | How do Thrust, Push and Pull Affect Objects
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- KS2 Science
- Forces 02
Skis are designed to have low friction.
Children in KS2 will study forces such as gravity, thrust or friction. Whatever the force, it has either a push or a pull effect on objects around it. This is the second of three Science quizzes looking at the different types, and the effects, of these push and pull forces.
There are many types of force, such as thrust, magnetism and gravity. The famous scientist Galileo wanted to know whether gravity exerted the same force on all objects whatever their mass (the amount of matter an object contains). He dropped a cannonball and a small stone off the top of the tower of Pisa — and both hit the ground at the same time, showing that gravity always has the same force on all objects. Feathers only fall more slowly because of friction with the air. On the Moon a feather and a hammer fall at the same rate. Many people don’t believe this until they try a similar experiment themselves.
See how much you know about gravity, friction and thrust by trying this quiz on the forces of push and pull.
Why do trainers have rough-textured soles?
Rough-textured soles make trainers more ‘slippery’
No one wants shoes which don’t leave interesting footprints
Rough-textured soles help trainers to ‘grip’ surfaces better
People like to show off their shoe soles
If an object is stationary (not moving), what are the forces acting on it?
The forces are balanced
The forces are unbalanced
The forces are moving
The forces are unmoving
Which of these objects is designed to have low friction?
When a bowl is sitting on a table, which forces are said to be ‘balanced’?
Gravity and air resistance
Upthrust and gravity
Friction and magnetism
Magnetism and air resistance
What forces are exerted by magnets?
Pushes and pulls
Neither pushes nor pulls
‘Compressing’ a spring means which of these?
To push it inwards
To pull it outwards
To tie it into a knot
To send it down the stairs
What effect does air resistance have on a falling object?
It causes the falling object to speed up
It pushes the falling object sideways
It has no effect
It slows the falling object down
Which of these would not be a result of applying force to a material?
The material is stretched
The material is compressed
The material is twisted
The material is changed into a new material
Different Newtonmeters are used to measure different amounts of force. A Newtonmeter designed to measure large forces will have what type of spring?
A long, thin, very flexible spring
A thick spring that is very stiff
A short, but very flexible spring
What does friction cause?
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11 different types of forces | New-Science.ru
In physics, force can be defined as a push or pull on any object that has mass. This changes the movement of the object.
In other words, a force causes an object with mass to change its direction and speed.
The two great physicists Isaac Newton and Galileo Galilei described the behavior of forces mathematically. In 1638, Galileo performed an experiment on an inclined plane that revolutionized the way force was measured. Five decades later, Newton developed the laws of motion that laid the foundation for classical mechanics.
Because force has both magnitude and direction, it is a vector quantity. It is represented by the symbol F and is measured in the SI unit of Newton (N).
Forces can be divided into two groups depending on their application:
- Contact force: acts on the body directly or through a medium.
- Non-contact force: acts through spaces without direct contact with the body.
To better explain this phenomenon, we have described all the different types of forces with examples. Let’s start with the four fundamental forces in nature.
1. The gravitational force
G is the universal gravitational constant, which varies with different astronomical bodies.
Type: contactless force
Gravitational force is what attracts two objects with mass. It affects every object, including you, in the universe.
The magnitude of the gravitational force exerted by objects on each other is «directly proportional to the product of their masses and inversely proportional to the square of the distance between them.» The more massive the objects and the smaller the distance between them, the higher the force.
This is the weakest of the four fundamental forces found in nature.
Although the gravitational force does not have a significant effect on the subatomic scale, it is the dominant interaction on the macroscopic scale and significantly affects the formation, structure and trajectory of celestial bodies.
Example: gravity makes an apple fall from a tree; it makes the moon revolve around the earth; it keeps the gases in the sun.
2. Electromagnetic force
Type: Non-contact force
This is the kind of interaction that occurs between electrically charged particles. Electromagnetic fields (produced by moving electric charges) carry an electromagnetic force.
Electricity and magnetism are related: flowing electrons create magnetism and moving magnets generate electricity. The relationship between them is very well explained by James Clerk Maxwell and quantified in his equations.
Example: The most common example of electromagnetism is light, as it propagates (radiates) through space, carrying electromagnetic radiation energy.
The next most common example would be the forces acting between electrically charged atomic nuclei and the electrons of atoms.
3. Strong nuclear force
Protons and neutrons are held together by the strong nuclear force
Type: Non-contact force
In nuclear and particle physics, the strong force is responsible for the structural integrity of atomic nuclei. Since all protons have a positive charge, they repel each other. The strong nuclear force holds these repulsive protons together so they can form an atomic nucleus.
About 99% of the mass of a neutron or proton is the result of the energy of a strong force field.
This is the strongest force in nature, acting at a distance of 1 femtometer ( 10–15 m). It is almost 137 times stronger than electromagnetism and 100 billion (1038) times stronger than the force of gravity.
Example: The strong nuclear force binds quarks to hadronic particles such as the proton and neutron to create the atomic nucleus. It is the force that binds ordinary matter together.
On a larger scale, it is used in nuclear power plants to produce heat to generate electricity. It is also responsible for the enormous destructive power of nuclear weapons. Because of this force, nuclear weapons release an extreme amount of energy when they explode.
Weak nuclear force
Radioactive decay of a particle
Type: Non-contact force
In nuclear physics, the weak force refers to the interaction between subatomic particles that causes the radioactive decay of atoms. More specifically, it is responsible for the decay of some nucleons into leptons and other types of hadrons.
Its field strength is about 10 13 times smaller than that of the strong nuclear force. However, it is significantly stronger than the gravitational force at short distances.
Example: The best known effect of the weak force is beta decay (of neutrons) and the associated radioactivity. It occurs in several different reactions, including solar burning and radiocarbon dating.
These are the four fundamental (contactless) forces from which everything else comes. They keep the stars burning and the planets spinning. Without them, the universe as we know it would not exist, and even if it did, it would be a completely different place.
Now let’s move on to minor forces that result from direct physical interaction between two objects.
5. Applied Force
Type: Contact Force
Type: Contact Force
As the name suggests, this is the force you apply to an object. An object begins to move when the amount of force overcomes the object’s inertia.
The body remains at rest or in uniform motion in a straight line, unless an external force is applied to them, which changes the state of motion and the direction of the body. The acceleration of a body is directly proportional to the applied force.
Example: Force applied to the box by a person.
6. Friction force
Type: Contact force
The surface force opposing the relative motion of a body is called the friction force. Because no object is perfectly smooth in the real world, there is always some friction between two surfaces. Its value is proportional to the coefficient of friction of the surface material.
The two main types of friction forces are static (the force of friction against a stationary object) and kinetic (the force of friction against a moving object). Air resistance is also the frictional force that acts on objects as they move through the air.
It always acts in the opposite direction of motion and converts kinetic energy into heat energy (work into heat). In general, friction is a critical and desirable force that provides traction for easier movement over land.
Example: An example of friction is sliding cabotage across the table, sliding two cards in a deck against each other and rubbing the hand to generate heat.
7. Normal Force
Type: Contact force
When two surfaces are in contact, they exert a normal force on each other. The term «normal» refers to perpendicular. This means that the force is directed perpendicular to the two contact surfaces.
Example: When the laptop is on a table, normal force keeps it from falling over the table. The gravitational force of the Earth is pulling the laptop down, but since it isn’t actually falling, there must be a force constantly pushing it up. This is what we call normal force.
It comes from an electromagnetic force: the laptop’s electrons push the table’s electrons. Because the electrons are all negatively charged, they don’t get much closer together and the laptop rests on the top of the table.
8. Tension force
Type: Contact force
Tension force is usually transmitted through a wire, cable, string or rope when it is pulled tightly by forces acting from opposite ends. The force is directed along the length of the cable.
Tension can also be defined as the action-reaction of a pair of forces acting at each end of a cable. This is the opposite of compression.
Example: a rope pulling a box or a box hanging from a rope would be a great example of tension (in the rope).
9. Elastic force
Type: Contact force
Elastic force is the force exerted by a stretched or compressed string on an object attached to it.
The ability of a spring to withstand a distorting effect and return to its original state when the effect is removed depends on its material, the number of turns and the diameter of the wire forming the turns. Typically, these characteristics are quantified in a parameter called the spring constant «k».
For all Hooke’s Law springs, the magnitude of the force is directly proportional to the spring constant (k) and the compressed/stretched length (x).
Example: Automotive shock absorbers are made from springs. They are designed to absorb shock impulses by converting the kinetic energy of an impact into another form of energy (such as heat), which is then dissipated.
10. Centripetal force
Type: Non-contact force
Centripetal force acts on objects accelerating in a circular motion. This is the force that causes an object to follow a curved path.
The direction of this force is always directed to the fixed point of the instantaneous center of curvature of the trajectory and is orthogonal to the movement of the object.
Example: The two most common examples of centripetal force are the rotation of a car and the Earth orbiting the Sun. In the first case, the centripetal force is provided by friction between the wheels and the ground, and in the second, by gravity.
11. The force of inertia
Type: Contact force
Inertia (also called inertial force) are obvious forces acting on the masses, the movement of which is described using a non -inertial reference system, including a rotating reference system.
This takes effect when the reference frame starts accelerating. The term «inertial force» has a precise meaning for Newtonian mechanics — in fact, it is always proportional to the mass of the object on which it acts.
Example: The forces you experience in a moving car are everyday examples of inertial forces. As the car accelerates forward, it pushes you back into the seat. When the car makes sharp turns, it throws you from side to side. These influences arise because the natural frame of reference for a given situation is itself accelerating.
Types of forces around us
In the world around us, there are countless bodies that interact with each other. But, despite this variety of forces, it is customary to single out several of their types in particular.
Elastic force is the force that occurs in the body when its shape or size changes. This happens if the body is compressed, stretched, bent or twisted. For example, an elastic force arose in a spring as a result of its compression and acts on a brick.
The elastic force is always directed opposite to the force that caused the change in the shape or size of the body. In our example, the fallen brick compressed the spring, that is, it acted on it with a downward force. As a result, an elastic force appeared in the spring, directed in the opposite direction, that is, upwards. We can confirm this by observing the rebound of a brick.
Gravity is the force with which all bodies in the world are attracted to each other (see § 2-a). Gravity is a kind of gravity — the force with which a body located near a planet is attracted to it. For example, a rocket standing on Mars is also affected by gravity.
Gravity is always directed towards the center of the planet. The figure shows that the Earth is pulling the boy and the ball with forces directed downward, that is, towards the center of the planet. As you can see, the «down» direction is different for different places on the planet. This will be true for other planets and cosmic bodies as well. We will study the force of gravity in more detail in § 3-d.
Friction force is the force that prevents one body from slipping over the surface of another. Consider the figure. Sudden braking of the car is always accompanied by a «squeal of brakes». This sound is caused by the tires slipping on the pavement. In this case, the tires are strongly erased, since a friction force acts between the wheels and the road, preventing slippage.
The friction force is always directed opposite to the direction of (possible) sliding of the considered body over the surface of another. For example, when a car brakes hard, its wheels slip forward, which means that the friction force acting on them on the road is directed in the opposite direction, that is, backwards.
The force of friction arises not only when one body slides over the surface of another. There is also static friction force. For example, pushing off the road with a boot, we do not observe its slippage.