1. Forces

2. Force is a push or a pull. is a push or a pull. a force is described by its strength and by the direction in which it acts. a force is described by its strength and by the direction in which it acts. The strength of a force is measured in the SI unit called the newton (N). The strength of a force is measured in the SI unit called the newton (N).

3. Balanced forces Balanced Forces-Equal forces acting on one object in opposite directions. Balanced Forces-Equal forces acting on one object in opposite directions. Balanced Forces Balanced Forces Balanced forces acting on an object do not change the object’s motion. Balanced forces acting on an object do not change the object’s motion. When equal forces are exerted in opposite directions, the net force is zero. forces cancel out. When equal forces are exerted in opposite directions, the net force is zero. forces cancel out.

4. Unbalanced Forces Forces that produce a nonzero net force, which changes an object’s motion. Forces that produce a nonzero net force, which changes an object’s motion. can cause an object to start moving, stop moving, or change direction. can cause an object to start moving, stop moving, or change direction. Unbalanced forces acting on an object result in a net force and cause a change in the object’s motion. Unbalanced forces acting on an object result in a net force and cause a change in the object’s motion.

5. Net Force When the two people push the box in opposite directions, the net force on the box is the difference between their individual forces. When the two people push the box in opposite directions, the net force on the box is the difference between their individual forces. The overall force on an object when all the individual forces acting on it are added together The overall force on an object when all the individual forces acting on it are added together The net force determines whether an object moves and also in which direction it moves. The net force determines whether an object moves and also in which direction it moves. Net Force Example Net Force Example

6. Friction The force that one surface exerts on another when the two surfaces rub against each other. The force that one surface exerts on another when the two surfaces rub against each other. In general, smooth surfaces produce less friction than rough surfaces. The strength of the force of friction depends on two factors: how hard the surfaces push together and the types of surfaces involved. In general, smooth surfaces produce less friction than rough surfaces. The strength of the force of friction depends on two factors: how hard the surfaces push together and the types of surfaces involved. Friction

7. Types of Friction Types of Friction Sliding friction- Friction that occurs when one solid surface slides over another. Sliding friction- Friction that occurs when one solid surface slides over another. Rolling friction- Friction that occurs when an object rolls over a surface. Rolling friction- Friction that occurs when an object rolls over a surface. Fluid friction- Friction that occurs as an object moves through a fluid. Fluid friction- Friction that occurs as an object moves through a fluid.

8. Newton’s laws Newton’s first law of motion- states that an object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless it is acted upon by an unbalanced force. Newton’s first law of motion- states that an object at rest will remain at rest, and an object moving at a constant velocity will continue moving at a constant velocity, unless it is acted upon by an unbalanced force. Inertia-The tendency of an object to resist any change in its motion.( depends on mass) ie. friction Inertia-The tendency of an object to resist any change in its motion.( depends on mass) ie. friction

9. Newton’s Laws Newton’s second law of motion- acceleration depends on the object’s mass and on the net force acting on the object. Newton’s second law of motion- acceleration depends on the object’s mass and on the net force acting on the object. Newton’s third law of motion- states that if one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. Newton’s third law of motion- states that if one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. Action-Reaction forces Action-Reaction forces

10. Gravity The force that pulls objects toward each other. The force that pulls objects toward each other. Two factors affect the gravitational attraction between objects: mass and distance. Two factors affect the gravitational attraction between objects: mass and distance. –The more mass an object has, the greater its gravitational force. –The farther apart two objects are, the lesser the gravitational force between them.

11. Center of Mass The center of gravity (mass)- is the point where all the weight of the object can be considered to be concentrated. The center of gravity (mass)- is the point where all the weight of the object can be considered to be concentrated. To balance an object ( see saw) you would need to find the center of mass To balance an object ( see saw) you would need to find the center of mass

12. Air and Gravity Free Fall- The motion of a falling object when the only force acting on it is gravity. Free Fall- The motion of a falling object when the only force acting on it is gravity. Air resistance- The fluid friction experienced by objects falling through the air. Air resistance- The fluid friction experienced by objects falling through the air. Projectile- An object that is thrown. Projectile- An object that is thrown.

13. Weight v. Mass Weight- The force of gravity on an object at the surface of a planet. Weight- The force of gravity on an object at the surface of a planet. Mass- Amount of matter in an object Mass- Amount of matter in an object