Forces

What Is a Force?

• Force- a push or a pull that acts on an objecto 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

o 1 N = 1 kg*m/s2

Representing Force

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

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

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

Friction

• A force that opposes the motion of objects that touch as they move past each other

• 4 main types of friction:1.) static friction2.) sliding friction3.) Rolling friction4.) fluid friction

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

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

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

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

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

Falling Objects

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

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

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