Force: It is a pull or a push that is applied to an object.
Forces affect different objects in two different ways Contact forces Noncontact forces
Contact forces In contact forces, the two objects need to contact each other
Noncontact forces In noncontact forces, the two objects don’t need to contact each other
How things move?
Motion It is a change in the position of an object compared to another object
Forces can pull or push objects in different directions
Forces can pull or push objects in different directions
Some forces are Weak Strong
Types of forces Magnetism Wind push objects Gravity You squeeze a spring
Magnetism
Magnetism It is an invisible force of attraction or repulsion between two magnets or between a magnet and an object.
Magnetism It is a force that attracts metal objects made of iron, nickel or cobalt by pulling on them
attract repel repelattract repelattract
Wind
Wind pushes on the blades of a wind turbines so it moves
Friction
Friction It is a force that opposes the motion of a body across a solid surface, liquid or a gas.
Friction It is generated between two touching surfaces
Friction slows the movement of objects
Brakes pull back the movement of the tires by friction
Types of friction force
Air friction It is a force that opposes the movement of an object as it passes through air.
Air friction When sky driver opens his parachute, the parachute gets filled with air, the air resistance pulls him backward and slows its fall to the Earth’s surface.
If we throw both of them, the ball falls faster The feather takes long time because its shape affected by the air resistance.
Law of motion The force of gravity is constant and acts on all objects in the same way
Spring
When you push a spring, it springs back when you leave it free
Gravity
Gravity exerts a pulling force only
attract repel repelattract Magnet exerts push or pull forces
Gravity
Gravity Gravity is the force of attraction that exists between objects that have mass
Gravity is a force? Because we can see its effect
Bigger planets have more gravity than smaller ones.
Earth is bigger (has more mass) than the moon
So Earth has stronger gravity than the moon, so Earth attracts the moon to stay in a fixed orbit around the Earth.
If there is no gravity, the moon would float off into space
The force of gravity keeps the planets revolve in their orbits around the Sun.
What goes up must come down
When you throw object in the air, its direction changes and fall down back to the ground due to gravity
Gravity changes the direction of the balls
A boy on a slide moves down due to gravity
If there is no gravity the boy will not be held on the slide
Pouring oil and falling down toward the ground Give reasons for Due to gravity
In basketball game, each time the ball is thrown in the air, it falls down toward the ground. Give reasons for Due to gravity that pulls the ball down toward the ground.
Gravity pulls objects toward the center of the Earth
Gravity affects two objects even if they don’t touch each other Ex: Earth attracts the moon to revolve in a certain orbit
The Sun pulls all planets around it.
Gravity keeps our planet in an orbit around the Sun.
Gravity keeps our atmosphere around Earth..
Gravity pulls everything and holds them to the ground toward the center of the Earth. On Earth
Skydivers and their parachutes are pulled downward toward Earth’s surface
Gravity affects moving objects and static objects
A boy sits on a chair is affected by gravity
Mass and gravitational force
Gravity of the object increases as its mass increases and vice versa
Gravity is a force of objects with more mass that pulls objects with less mass toward them.
We can’t see gravity but you can see its effects
The mass of the moon becomes twice its real mass The moon would have more gravity, so it would pull closer to Earth and it might even crash into Earth What happens if...........?
Distance and gravitational force
When the distance between two objects increases the gravity decreases
The distance between the moon and the Earth becomes twice than it is. The gravity between them decreases and become smaller What happens if...........?
Our solar system, consists f the Sun and group of planets revolve around it.
Nicolas Copernicus, in 1543 said that the Earth revolves around the Sun
In the solar system, each planet revolves around the Sun in a fixed path called an orbit.
The orbit has oval (ellipse) shape
Earth revolves around the Sun at a speed nearly 107000 km per hour
What keeps the planets revolve around the Sun on fixed orbits?
Gravity is the invisible attraction or pulling force that holds all the planets in their places
The great gravity of the Sun keeps the planets revolving in fixed orbits.
If there were no gravity, the planets would fly off into space
The sun is the only center of motion in the solar system Because the Sun is bigger than all the other objects so its gravity pulls the other plants Give reasons for: