WEEK 11
Posted: Wed Jun 17, 2015 4:39 am
LESSON 26
TOPIC: Calculation on gravitational force
CONTENT: Calculation of gravitational force
Balanced and unbalanced forces
Friction
Advantages and disadvantages of friction
Gravitational force:
Is the force with which the earth pulls all objects towards its centre. It is also called force of gravity.
If a piece of stone and feather are allowed to fall at the same time, the stone reaches the ground first. This means that rate of force depend on body weight or mass.
Calculation of gravitational forces:
The unit of force is Newton (the symbol is N). The unit was named after Sir Isaac Newton who first discovered the facts about gravity. The weight of a body is the force the earth exerts on it. All forces are measured in Newton.
To calculate gravitational force (Gf). The following formula is used.
Gf = mgh
m = mass of the object measured in kilogram (Kg)
g = acceleration due to gravity measured in meter per seconds square (m|s2)
h = height of object measured in meter (M)
This force can be measured using a calibrated spring balance
Example:If you lift an object from the surface of the ground, you do work in opposing gravity. Suppose you lift an object of mass 2kg from the ground to height of 2m, what is the work done in lifting the object?
Solution:
The work done in lifting the object is calculated by using the formula mgh where:
W = work done = mgh
m = mass of the object in kg
g = force of gravity
h = height of object moved in meters.
g = 9.8m/s2
mgh = 2 x 2 x9.8 Newton per sec.
= 39.2Joules.
Spring balance
Distance through which the spring is pulled is a measure of the gravitational force.
F=Mg=Ke
M= mass of the object; g= acceleration due to gravity ;K= Force constant and e = extension (distance) of the spring.
https://youtu.be/0hOuNtRMSAI
Balanced and Unbalanced forces:
If a body is at rest, it means that all the forces acting upon it are equal and opposite. This is a balanced force.
But on the other hand if the forces acting on it are not equal the forces are unbalanced, the body will move in the direction of this unbalanced force.
Friction:
The force that tries to stop a body from moving is called friction. The force it exerted on the moving body is called frictional force. Friction can be reduced by lubrication i.e. adding oil and grease placed between the two surfaces in contact. The oil and grease are called lubricants.
LESSON 27
Uses\ advantages of friction
1. Without friction we cannot move and when we start moving we would not be able to stop.
2. Friction makes cars to move on the road. The tier of a car have rough surfaces so that when the
engine of the car makes the wheels go round, they grip on the surface of the road. If tire and roads
were so smooth there will be no friction between them, the car would not move.
Disadvantages of frictions
3. It causes wear and tear on the moving parts of machines
4. It causes unpleasant noise .
5. It increases the cost of maintenance
6. It causes heat in any engine which can lead to break down of the engine.
How to reduce friction.
Friction is reduced by application of greases and oils called Lubricants. Lubricant is placed between the two surfaces in contact
Evaluation:
1. Define friction
2. State the advantage and disadvantages of friction
3. State the formula for calculating gravitational force and explain the formula.
4. A ball of 25kg is lifted up to a height of 10meters;calculate the gravitational force using the formula G = mgh
Note: g is a constant. 9.8m/s2
Reading assignment:
Read Basic Science Made Easy pages 114-119 and STAN pages 153-160.
Assignment:
Solve the following problems;
1. Calculate the work done when an object 7kg was raised to a height 10m.
2. A ball of 25kg is lifted up to a height 12m; calculate the gravitational force
using the formula Gf = mgh. (g=9.8m\s2)
TOPIC: Calculation on gravitational force
CONTENT: Calculation of gravitational force
Balanced and unbalanced forces
Friction
Advantages and disadvantages of friction
Gravitational force:
Is the force with which the earth pulls all objects towards its centre. It is also called force of gravity.
If a piece of stone and feather are allowed to fall at the same time, the stone reaches the ground first. This means that rate of force depend on body weight or mass.
Calculation of gravitational forces:
The unit of force is Newton (the symbol is N). The unit was named after Sir Isaac Newton who first discovered the facts about gravity. The weight of a body is the force the earth exerts on it. All forces are measured in Newton.
To calculate gravitational force (Gf). The following formula is used.
Gf = mgh
m = mass of the object measured in kilogram (Kg)
g = acceleration due to gravity measured in meter per seconds square (m|s2)
h = height of object measured in meter (M)
This force can be measured using a calibrated spring balance
Example:If you lift an object from the surface of the ground, you do work in opposing gravity. Suppose you lift an object of mass 2kg from the ground to height of 2m, what is the work done in lifting the object?
Solution:
The work done in lifting the object is calculated by using the formula mgh where:
W = work done = mgh
m = mass of the object in kg
g = force of gravity
h = height of object moved in meters.
g = 9.8m/s2
mgh = 2 x 2 x9.8 Newton per sec.
= 39.2Joules.
Spring balance
Distance through which the spring is pulled is a measure of the gravitational force.
F=Mg=Ke
M= mass of the object; g= acceleration due to gravity ;K= Force constant and e = extension (distance) of the spring.
https://youtu.be/0hOuNtRMSAI
Balanced and Unbalanced forces:
If a body is at rest, it means that all the forces acting upon it are equal and opposite. This is a balanced force.
But on the other hand if the forces acting on it are not equal the forces are unbalanced, the body will move in the direction of this unbalanced force.
Friction:
The force that tries to stop a body from moving is called friction. The force it exerted on the moving body is called frictional force. Friction can be reduced by lubrication i.e. adding oil and grease placed between the two surfaces in contact. The oil and grease are called lubricants.
LESSON 27
Uses\ advantages of friction
1. Without friction we cannot move and when we start moving we would not be able to stop.
2. Friction makes cars to move on the road. The tier of a car have rough surfaces so that when the
engine of the car makes the wheels go round, they grip on the surface of the road. If tire and roads
were so smooth there will be no friction between them, the car would not move.
Disadvantages of frictions
3. It causes wear and tear on the moving parts of machines
4. It causes unpleasant noise .
5. It increases the cost of maintenance
6. It causes heat in any engine which can lead to break down of the engine.
How to reduce friction.
Friction is reduced by application of greases and oils called Lubricants. Lubricant is placed between the two surfaces in contact
Evaluation:
1. Define friction
2. State the advantage and disadvantages of friction
3. State the formula for calculating gravitational force and explain the formula.
4. A ball of 25kg is lifted up to a height of 10meters;calculate the gravitational force using the formula G = mgh
Note: g is a constant. 9.8m/s2
Reading assignment:
Read Basic Science Made Easy pages 114-119 and STAN pages 153-160.
Assignment:
Solve the following problems;
1. Calculate the work done when an object 7kg was raised to a height 10m.
2. A ball of 25kg is lifted up to a height 12m; calculate the gravitational force
using the formula Gf = mgh. (g=9.8m\s2)