Forces

1. Forces

2. Force • a push or pull that can cause an object to move, or change its speed or direction • measured in Newtons (N)

3. Contact Forces • a force that results from the physical contact between two objects • Friction • force that opposes motion between two surfaces that are touching • ex. pushing a box over carpet • Tension • force pulls against the materials that make up an object • ex. cables on a bridge • Buoyancy • an upward force exerted on an object by a fluid • ex. bobbing buoy

4. Forces Acting at a Distance • objects do not have to touch each other to exert this force • Gravity • force of attraction due to the masses of the objects • ex. the Sun and planets • Magnetic Force • force exerted by magnetized objects • ex. compass needle • Electric Force • force of attraction or repulsion between charged particles • ex. rubbing a balloon on your hair

5. Gravity • Gravity is a universal forcebecause gravity affects all matter, therefore all objects are attracted to one another. • The size of a gravitational force between objects depends on the mass of the object and the distance between them

6. Weight and Mass • Weight • measure of the gravitational pull on an object • Mass • amount of matter in an object • does not change • ex. on the moon your weight is less, but your mass is the same

7. Gravity and Falling Objects • GailileoGalilei discovered that an object’s mass does not affect the rate at which it falls. • Acceleration depends on force and mass: • objects with more mass take more force to fall, and objects with less mass take less force to fall, therefore the acceleration due to gravity is the same for all objects • the rate is 9.8 m/s²

8. Velocity of Falling Objects • Calculate the change in velocity of an object (Δv) by using this equation: Δv = g × t • g = the acceleration due to gravity (9.8 m/s²) • t = time it takes the object to fall

9. Air Resistance • the force that opposes the motion of objects through air • Terminal Velocity • objects continue accelerating as they fall until the upward force of air resistance equals the downward force of gravity, then they fall at a constant velocity (terminal velocity)

10. Projectile Motion • the curved path an object follows when it is thrown or propelled near Earth’s surface • Two components: • horizontal motion (throwing or propelling) • vertical motion (gravity)

11. Net Force • the combination of all the forces acting on an object • Acting in the Same Direction • simply add all the forces together • direction of movement is in the direction of force

12. Net Force • Acting in Opposing Directions • subtract the smaller force from the larger force • if the net force is zero than the forces are balanced and there is no movement • if the net force is greater than zero the forces are unbalanced and the direction is toward the greater force

13. Balanced/Unbalanced Forces Balanced Forces Unbalanced Forces 600 N – 550 N = 50 N movement to the left 600 N – 600 N = 0 N no movement

14. Net Force Diagrams • Johnny pulls a wagon along the sidewalk with a force of 90 N. The friction of the sidewalk is 20 N. What is the net force and in what direction is the movement? • Paul and Jason are moving a refrigerator. Paul is pushing it to the right with a force of 120 N, while Jason is pulling it to the right with a force of 200 N. What is the net force and in what direction is the refrigerator moving?

15. Inertia • the tendency of an object to resist motion • the greater an object’s mass, the greater its inertia

16. Inertia and Motion • Objects at Rest • objects at rest stay at rest unless acted upon by an unbalanced force • ex. bowling pins • Objects in Motion • objects in motion stay in motion unless acted upon by an unbalanced force • the unbalanced force of friction acts on almost all moving objects • ex. rolling bowling ball