Gravitational force is a force that can act at a distance from an object. It is the force of attraction between things and the Earth.
Effects of gravitational force
Gravitational force pulls the motorcycle back as
he tries to ride the motorcycle up to the mountain.
Weight of an Object
All objects on the Earth have weight. Objects have weight because of the gravitational force acting between them and the Earth.
Differences:
Similarities: -------->Weight is:
Weight--> | -a force
Weight--> | -a force
Both can be measured--| -the gravitational force acting on an object
Mass---> | -different at different places. The weight of an object is different
| on the Earth, the moon and other planets
-------->Mass is:
-not a force
-the amount of matter in an object
-constant. The mass of an object is the same, regardless of
where the object is.
19.2 Frictional force
Frictional force is a force that opposes motion. It is produced when two surfaces rub against each other.
Frictional force has many effects, it can:
@slow down and stop moving objects.
@prevent an object from starting to move.
@affect the movement of objects on different surfaces.
1.Frictional force can slow down and stop moving objects
When we push a toy car, the toy car travels for a short distance then comes to a stop. This is because there is frictional force acting between the tyres of the toy car and the table.
2.Frictional force may prevent an object from starting to move
when we try to push a car, we may find that it does not move. This is because frictional force is opposing the movement of the car.
3.Frictional force affects the movement of objects on different surfaces
There is greater frictional force between rough surfaces then between smooth surfaces. So, objects move more slowly on rough surfaces than on smooth surfaces.
Air resistance and Water resistance
Frictional force is also produced when objects move through air and water.
1.Air resistance
The frictional force acting on objects as they move through air or as air flows around them is called Air resistance. Air resistance pushes against a moving object and slows it down.
2.Water resistance
The frictional force acting on objects as they move through water is called water resistance. Water resistance pushes against a moving object and slows it down.
Frictional forces can be useful and can cause problems
We can see frictional forces acting around us all the time. Sometimes, frictional forces can be useful. At other times they can cause problems.
1.Frictional forces can be useful
Frictional forces is useful in our daily lives. Without frictional force, there will be no grip.
2.Frictional force can cause problems
Although frictional force is useful in many instances in our daily lives, it can also be a problem.
The moving parts of the machine rub against each other, creating frictional force. Machines need extra energy to work against friction. This causes excess heat to be produced. Due to this, the parts of the machine get worn out more easily.
Friction can cause problems because it causes objects to:
*Slow down
*Over heat
*Wear out
Ways to overcome friction
We can reduce friction between surfaces in many ways including the use of:
+ Lubricants
+ Oil
Frictional force is a force that opposes motion. It is produced when two surfaces rub against each other.
Frictional force has many effects, it can:
@slow down and stop moving objects.
@prevent an object from starting to move.
@affect the movement of objects on different surfaces.
1.Frictional force can slow down and stop moving objects
When we push a toy car, the toy car travels for a short distance then comes to a stop. This is because there is frictional force acting between the tyres of the toy car and the table.2.Frictional force may prevent an object from starting to move
3.Frictional force affects the movement of objects on different surfaces
There is greater frictional force between rough surfaces then between smooth surfaces. So, objects move more slowly on rough surfaces than on smooth surfaces.
Air resistance and Water resistance
Frictional force is also produced when objects move through air and water.
1.Air resistance
The frictional force acting on objects as they move through air or as air flows around them is called Air resistance. Air resistance pushes against a moving object and slows it down.2.Water resistance
The frictional force acting on objects as they move through water is called water resistance. Water resistance pushes against a moving object and slows it down.
Frictional forces can be useful and can cause problems
We can see frictional forces acting around us all the time. Sometimes, frictional forces can be useful. At other times they can cause problems.
1.Frictional forces can be useful
Frictional forces is useful in our daily lives. Without frictional force, there will be no grip.
2.Frictional force can cause problems
Although frictional force is useful in many instances in our daily lives, it can also be a problem.
The moving parts of the machine rub against each other, creating frictional force. Machines need extra energy to work against friction. This causes excess heat to be produced. Due to this, the parts of the machine get worn out more easily.
Friction can cause problems because it causes objects to:
*Slow down
*Over heat
*Wear out
Ways to overcome friction
We can reduce friction between surfaces in many ways including the use of:
+ Lubricants
+ Oil
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