Forces. Brought to you by:

Transcription

1 Forces Brought to you by:

2 Objects have force because of their mass and inertia Mass is a measure of the amount of matter/particles in a substance. Mass is traditionally measured with a balance. Inertia is an object s resistance to a change in motion (start, stop, or turn). Inertia is measured using mass.

3 What is Force? A push or pull of one object on another Force is a vector quantity, meaning whenever calculating force you must give: -- an amount -- a unit -- a direction Example: 100 N south Amount / unit / direction Force is represented as an arrow

4 Calculating Force Force is a measure of how strong the push or pull is on one object by another Objects with more mass push or pull with more force Objects with less mass push or pull with less force Force is not just based on mass, so a different type of unit must be used

5 Units for Force Mass is a factor with force, but so is speed and acceleration in calculating force, so Force = mass x acceleration When calculating force, the unit of Newtons (N) must be applied 1 N = 1 kg x m/s 2 YOU MUST ALWAYS remember that mass must be in kilograms (kg) when calculating force

6 Types of Forces There are many different types of forces: Contact forces: normal, friction, compression, tension Non-contact forces: Electromagnetic and gravity

7 Balanced Forces When all the forces acting upon an object are equal in strength, but opposite in direction, the forces are called balanced Balanced force: Forces cancel each other out and there is no net force and no change in motion Net force: The sum total of all the forces acting upon an object Example: 7 N South 7 N North Net Force = 0

8 Unbalanced Forces When the forces acting upon an object are not equal in strength, not in opposite directions, or both, the forces are said to be unbalanced Unbalanced forces: Forces do not cancel each other out and there is a net force that causes a change in motion. To calculate unbalanced forces, add the forces going in the same direction together, and subtract all forces going in the opposite direction Example 1: 3 N South 7 N South 2 N Example 2: 5 N South North Net Force: Net Force: 10 N South 3 N North

9 Net Force = 0 Force Practice Problems 30 N South 55 N South Net Force = 85 N South 12 N South Net Force = 5 N North 7 N South 4 N South 4 N North

10 Forces Notes Part 2

11 Newton s 1st Law of Motion 1 st Law An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force.

12 Newton s 1st Law Objects on earth, unlike the Once airborne, unless acted on by an unbalanced force (gravity and air resistance), it would never stop! frictionless space the moon travels through, are under the influence of friction.

13 What is this unbalanced force that acts on an object in motion? There are four main types of friction: Sliding friction: ice skating Rolling friction: bowling Fluid friction (air or liquid): air or water resistance Static friction: initial friction when moving an object

14 Newton s 1st Law Don t let this be you. Wear seat belts! Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 m/hour.

15 Newton s 2nd Law of Motion 2 nd Law Force equals mass times acceleration.

16 Newton s 2 nd Law proves that different masses accelerate to the earth at the same rate, but with different forces. We know that objects with different masses accelerate to the ground at the same rate. However, because of the 2 nd Law we know that they don t hit the ground with the same force. F = ma 98 N = 10 kg x 9.8 m/s/s F = ma 9.8 N = 1 kg x 9.8 m/s/s

17 Newton s 3rd Law of Motion 3 rd Law For every action there is an equal and opposite reaction.

18 Newton s 3rd Law According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. For example, when you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.

19 There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces.

20 Newton s 3rd Law The baseball forces the bat to the left (an action); the bat forces the ball to the right (the reaction).

21 May the Force be with you!