Forces

1. Forces

2. What Is a Force? • Force- a push or a pull that acts on an object • Can cause a resting object to move, or it can accelerate a moving object • Forces are measured in Newtons (N) • One newton is the forces that causes 1 kg mass to accelerate at a rate of 1 meter per second each second • 1 N = 1 kg*m/s2

3. Representing Force • Forces can’t be seen, but their effects can. So we have come up with a way to represent forces

4. Forces can be combined • Forces in the same direction add together • Forces in opposite directions subtract from one another • The net force is the overall force acting on an object after the forces are combined

5. Balanced and Unbalanced Forces • When forces on an object are balanced, the net force in zero and there is no change in the object’s motion • When an unbalanced force acts on an object, the object accelerates

6. Friction • A force that opposes the motion of objects that touch as they move past each other • 4 main types of friction: 1.) static friction 2.) sliding friction 3.) Rolling friction 4.) fluid friction

7. Static Friction • Acts on object that are not moving • Always acts in the direction opposite to that of the applied force • You experience static friction every time you take a step

8. Sliding Friction • Force that opposes the direction of motion of an object as it slides over a surface - Less than static friction. Therefore, less force is needed to keep an object moving than to start it moving

9. Rolling Friction • Friction force that acts on rolling objects • 100 to 1000 times less than the force of static or sliding friction • Helps explain why professional movers use wheeled dollies to move heavy objects

10. Fluid Friction • Opposes the motion of an object through a fluid • Examples can be seen on a submarine moving through water or an airplane flying through air • You can feel fluid friction when stirring thick cake batter • Increases as the speed of the object moving through the fluid increases • Fluid friction acting on an object moving through the air is known as air resistance

11. Gravity • Force that acts between any 2 masses -attractive force—pulls objects together -does not require objects to be in contact -can act over long distances -Earth’s gravity acts downward toward the center of Earth

12. Falling Objects • Gravity causes objects to accelerate downward, whereas air resistance acts in the direction opposite to the motion and reduces acceleration

13. Falling objects • As objects fall to the ground, they accelerate and gain speed • Terminal velocity is the constant velocity of a falling object when the force air resistance equals the force of gravity -the doesn’t mean the objects stop in mid air…it just means it doesn’t accelerate anymore • Mass does NOT matter, all objects fall at the same rate

14. Projectile Motion • The motion of a falling object (projectile) after it is given an initial forward velocity. • Air resistance and gravity are the only forces acting on a projectile