5 - Forces

• Acceleration: The rate of change of velocity can be calculated from the gradient of a velocity-time graph.
• Atmosphere: The thin layer of air surrounding the Earth, which gets less dense with increasing altitude
• Braking Distance: The distance a vehicle travels under the braking force can be affected by adverse road and weather conditions as well as the condition of the vehicle
• Centre of Mass: The single point through which the weight of the object can be said to act
• Changes of Momentum: When a force acts on a moving object, or one an object that has the ability to move, a change of momentum will occur.
• Conservation of Momentum: The total momentum of a system before an event is always equal to the total momentum of the system after the event
• A Vector has magnitude and direction.
• A Scalar has just magnitude.
• Contact Forces: A force that occurs when objects are physically touching
• Generally, scalars cannot be negative, but vectors can be, as a certain direction is positive.
• Speed is a scalar.
• Displacement: A measure of how far an object moves in a given direction is the straight line between the starting and finishing points and is a vector quantity
• Velocity is a vector.
• Distance is a scalar.
• Distance: A measure of how far an object moves, that does not depend on direction and is therefore a scalar quantity
• Displacement is a vector.
• Time is a scalar.
• Acceleration is a vector.
• Elastic Deformation: Non-permanent deformation which allows the object to return to its original shape when the deforming forces are removed
• Force is a vector.
• Force is a vector.
• Acceleration is a vector.
• Mass is a scalar.
• Elastic Limit: The force beyond which an object will no longer deform elastically, and will instead deform plastically
• Momentum is a vector.
• Energy is a scalar.
• Elastic Potential Energy: The energy stored in a spring when it is stretched or compressed, due to the work done on the spring by the deforming force
• Imagine a ball thrown off a cliff, displacement is 0 at height of cliff, above the cliff the ball has positive displacement, and below the clifftop the ball has negative displacement.
• Equilibrium: An object is in equilibrium if the resultant force and resultant moment are both equal to zero
• Floating: An object will float if the volume of liquid it displaces has a greater weight than that of the object itself
• In long answer questions, you may be able to decide where the “0” point of a vector may lie, for example you could set zero to be bottom of cliff, so the ball will never have negative displacement.
• Fluid: A liquid or gas
• Forces: A push or pull that an object experiences due to the interaction with another object
• Force is a vector quantity
• Inertia: The tendency of an object to remain in its same state of uniform motion or rest
• Speed is only velocity when given a direction, so thrown 10 𝑚𝑚���� −1 is its speed but thrown 10 𝑚𝑚𝑠�� −1 at 30° above the horizontal is the velocity.
• Air Bags inflate instantaneously upon a crash, slowing down the head and increasing the time taken for the head to stop moving, reducing the force on the neck.
• Momentum is always conserved in a collision or explosion (where there are no external forces like friction, air resistance, electrostatic attraction etc.)
• Seatbelts prevent passengers from flying through the windshield during hard braking and decrease the force felt by stretching under large forces.
• Newton’s Second Law states that Force is equal to the rate of change of momentum.