Force & Motion Motion Motion is a change in the position of an object • Caused by force (a push or pull) Force A force is a a push or pull on an object • Measured in units called newtons (N) • Forces act in pairs Examples of Force: Ø Gravity Ø Magnetic Ø Friction Ø Centripetal Inertia Inertia is the tendency of an object to keep doing what it is doing • An object at rest will remain at rest until acted upon by an unbalanced force. • An object in motion will remain in motion until acted upon by an unbalanced force. Balanced Forces A balanced force is when all the forces acting on an object are equal (net force is zero) • Balanced forces do not cause a change in motion. How Can Balanced Forces Affect Objects? • Cause the shape of an object to change without changing its motion • Cause an object at rest to stay at rest or an object in motion to stay in motion (inertia) • Cause an object moving at a constant speed to continue at a constant speed What is an example of a balanced force? Unbalanced Forces An unbalanced force is when all the forces acting on an object are not equal • The forces can be in the same direction or in opposite directions. • Unbalanced forces cause a change in motion. How Can Unbalanced Forces Affect Objects? • Acceleration is caused by unbalanced forces: – slow down – speed up – stop – start – change direction – change shape What is an example of a unbalanced force? Net Force The Net force is he total of all forces acting on an object: – Forces in the same direction are added. • The object will move in the direction of the force. – Forces in opposite directions are subtracted. • An object will move in the direction of the greater force. Calculating Net Force 30 N 10 N http://commons.wikimedia.org/wiki/File:Jack-in-the-box.jpg A child was playing with a jack in the box. The lid pushed down with 10 N of force, while the spring pushed up with 30 N of force. What is the net force applied by the spring? In your notebook, calculate the net force and show all of your work. Check Your Answer 30 N 10 N http://commons.wikimedia.org/wiki/File:Jack-in-the-box.jpg A child was playing with a jack in the box. The lid pushed down with 10 N of force, while the spring pushed up with 30 N of force. What is the net force applied by the spring? 30 N up - 10 N down= 20 N up Calculating Net Force Tug of War Game 30 N 50 N Two competitors are playing tug of war. What is the net force? Which direction will the rope move? In your notebook, calculate the net force and show all of your work. Check Your Answer 30 N 50 N Two competitors are playing tug of war. What is the net force? Which direction will the rope move? 50 N to the right – 30 N to the left = 20 N to the right Mass and Weight • Mass is the amount of stuff (matter) in an object. – The mass of an object will remain the same anywhere in the universe. – Mass is measured in grams or kilograms. • Weight is the mass (kg) of an object multiplied by (x) the acceleration of gravity (9.8 m/s2). – The weight of an object depends on the gravitational pull at the location in the universe. – Weight is measured in newtons (N). .