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Presentation on theme: "Forces."— Presentation transcript:

1 Forces

2 What is force? A force is a push or a pull one body exerts on another body. Sometimes it is obvious a force has been applied, but other forces are not as noticeable. Forces can cause a change in motion.

3 Balanced forces When two or more forces act on an object at the same time, the forces combine to form the net force. Forces on an object that are equal in size and opposite in direction are called balanced forces.

4 BALANCED FORCES Balanced forces do not cause acceleration. (any change in speed or direction)

5 Unbalanced forces Unbalanced forces cause a change in motion.
Unbalanced forces cause an object to start moving, stop moving, or change direction. (an unbalanced force will cause an object to accelerate)

6 Unbalanced forces The forces acting on an object may not always be opposite in direction. The net force that acts on this box is found by adding the two forces together.

7 Force Diagrams In what direction and with how much force would the object travel?

8 Types of Forces A force can be either balanced or unbalanced.
Common types of force include gravity, magnetism, friction, air resistance, or centripetal force

9 Friction Suppose you give a skateboard a push with your hand.
According to Newton’s 1st law of motion, if the net force acting on an object is zero, it will continue to move in a straight line with constant speed. Does the skateboard keep moving forward with a constant speed after it leaves you hand?

10 Friction Recall that when an object slows down it is accelerating.
By Newton’s 2nd law of motion, if the skateboard is accelerating, there must be a net force acting on it. The force that stops the skateboard is friction.

11 Friction Friction is the force that opposes motion between two surfaces that are touching each other. The amount of friction depends on; 1: kinds of surfaces 2: the force pressing the surfaces together

12 Types of FRICTION Sliding friction- dry solid surfaces
Rolling friction- rolling over a surface Fluid friction- object moves through a liquid or gas.

13 Gravity Gravity’s attractive force depends on
1. the distance between the two objects 2. the mass of the two object Every object exerts a gravitational force on every other object

14 Gravity Isaac Newton formulated the law of universal gravitation, which he published in 1687. His law states that gravitational force= (constant) x (mass 1)x(mass 2) = G m1m2 (distance) d2 According to the law of universal gravitation, the gravitational force between two masses decreases rapidly as the distance between the masses increases.

15 GRAVITY Free fall- when the only force acting on a falling object is gravity. (9.8m/s/s) Do all objects regardless of mass fall at this rate? What about projectiles?


17 GRAVITY Air resistance- a type of fluid friction that objects falling through air experience. Paper vs.. Book Weight- The measure of the force of gravity on an object (scale) Mass- is a measure of the amount of matter in that object.

18 Weight Weight and mass are NOT the same.
Weight is a force and mass is a measure of the amount of matter an object contains. Weight and mass are related. Weight increases as mass increases.

19 Weight on different planets
The weight of an object usually is the gravitational force between the object and Earth. The weight of an object can change, depending on the gravitational force on the object.

20 Air resistance When an object falls towards Earth, it is pulled downward by a force called gravity. However, a friction-like force called air resistance opposes the motion of objects that move through air. Air resistance causes objects to fall with different accelerations and different speeds.

21 Air resistance The amount of air resistance on an object depends on the speed, size, and shape of the object. Air resistance, not the objects mass, is the reason feathers and leaves fall slower then pennies or apples.

22 What about circular motion???
Bucket Demonstration What is the centripetal force for a satellite? Centripetal- “center seeking” Centripetal force- any force that causes an object to move in a circle.


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