Unit 2: Forces Review Notes
– A push or pull measured in Newtons (N), vector quantity.
– Objects need a force to accelerate or slowdown.
4 Fundamental Forces
Gravitational Force- force of attraction between all objects
Electromagnetic Force- force caused by electric c
Strong Nuclear Force- force that holds protons and neutrons together in the nucleus
Weak Nuclear Force- force responsible for interactions, really small
– Forces that result from two objects in contact with one another
– If there is a net force, it could accelerate or decelerate an object
– If an object is at rest or moving at a constant speed, the net force is 0
Free Body Diagrams
– A diagram that shows all forces on an object
- “If the net force on an object is zero, the object will maintain its state of rest or constant velocity.”
– Objects at rest stay at rest
– Objects in motion tend to remain in motion
– Object moving at constant velocity has a net force of 0
– Object that changes its velocity is caused by change in net force
- When the net external force on an object is not 0, object accelerates in the direction of the net force. Acceleration is proportional to net force. Acceleration is inversely proportional to object’s mass.
– Gravitational field strength on Earth’s surface is 9.8m/s2 [down]
– Fg= m x g ¬ Used to find the force of gravity on an object
Example: Calculate the force of gravity acting on a 5.0kg ball.
Fg=m x g
Fg=5.0kg x 9.8m/s2[down]
– G is a constant= 6.67 x 10-11 (Nxm2)/kg2
Used in the equation:
– Acts between two surfaces
– Acts parallel to the surfaces and opposes forces that attempt to accelerate the object along the surface
– The force of friction is proportional to the normal force acting on an object
- Ff= μ x FN
μ= co-efficient of friction
Depends on the two material that are in contact
Static Friction- A force that tends to prevent a stationary object from moving or starting to move
Kinetic Friction- A force that acts against an object’s motion in a direction opposite to the direction of motion.
μs= co-efficient of static friction
μk= co-efficient of kinetic friction
Force of static friction is only has high as it needs to be. Cannot be greater than the force that it is opposing.
FFS= μs x FN
FFK= μK x FN
Fg= m x g