Grade 5 | Science | Unit 4 - Concept 1 - Lesson 4 - Gravity and Motion

Описание: Welcome dear students!
Gravity
• Gravity is a force that pulls objects with less mass toward objects with more mass.
• You cannot see gravity, but you know it is there because you can see its effects.
Examples:
• The Sun pulls all planets toward it.
• Gravity keeps our planet in an orbit around the Sun.
• Gravity keeps our atmosphere around Earth.
• On Earth, gravity pulls everything (such as humans, rocks, water bodies, animals, chairs, .... etc.) and holds them to the ground toward the center of Earth.
• Skydivers and their parachutes are pulled down toward Earth's surface.
Give a reason for:
Objects like balls drop to the ground after being thrown up into the air.
Due to Earth’s gravity that pulls them down toward the ground.
Magnetism, friction and air resistance
Magnetism
Magnetism is a force that attracts metal objects made of iron, nickel or cobalt by pulling on them.
Example:
Some iron nails can be attracted to a magnet due to its pulling force on them.
Friction
• Friction is a force generated between two touching surfaces.
• Friction slows the movement of objects.
Friction:
It is a force that opposes the motion of a body across a solid surface or through a gas or liquid.
Example:
A bicycle brake pulls back the movement of the tires by friction when the bicycle brake rub against the tires.
Air resistance
Air resistance is considered as a type of friction force.
Air resistance:
It is a force that opposes the movement of an object as it passes through air.
Example:
Skydiver releases parachute to slow his drop, where:
• When the skydiver opens his parachute, it gets filled with air due to the upward flow of wind forming air resistance to the parachute.
• The air resistance pulls the skydiver backward and slows his fall to Earth's surface.
Gravity and Motion
In this experiment, we will investigate the effect of gravity and air resistance on different objects.
Tools
• Two balls with the same size (Plastic ball without holes and Plastic ball with holes).
• Paper clip.
• Feather.
Steps
1. Stand on a chair and drop the two balls at the same time from the same height, then observe which ball will reach the floor first.
Observation:
The plastic ball without holes will reach the floor first.
2. Stand on a chair and drop the paper clip and the feather at the same time from the same height, then observe which one will reach the floor first.
Observation:
The paper clip will reach the floor first.
Conclusions
1. The plastic ball with holes took longer time to reach the floor, because it was slowed by upward-flowing air that passes through the holes causing the increase of the air resistance to the ball.
2. The feather took longer time to reach the floor, because it has a larger surface area than that of the paper clip, so the feather is affected by air resistance more than the paper clip.
• So that, air resistance is a factor that can slow down the falling objects.
Notes
1. If the surface area of an object increases, the air resistance that affects this object will increase and vice versa.
2. The effect of force of gravity is constant on all falling objects and acts on all objects in the same way, but the air resistance that affects the falling objects causes the difference in the time that the falling objects take to reach the floor.
Imagine that there is no air resistance on Earth:
So, if we drop a hammer and a paper at the same time from the same height, they will reach the floor at the same moment because gravity acts on all objects in the same way, where the mass or the shape of the objects would not matter.

#Gravity
#Magnetism
#Friction
#Air_resistance
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Mr. Raouf Ashraf