KPE160: Module 1| Exam Questions with Complete Solutions 100% Solved| Grade A+
Law of Reaction (Newton's 3rd Law) Material bodies push back when pushed. Whenever
one material body exerts a force on another material body through contact or adhesion, the
second body exerts a force of equal magnitude and opposite direction on the first body.
Collision The duration of contact between two or more bodies. Depends on elasticity - the
higher the elasticity, the lesser the duration of contact. Duration of contact is equal for both
bodies. Force (contact and reaction) is equal for both bodies, just in opposite directions. When
two or more material bodies are in contact (collide), they can accelerate or deform.
Impulse (J) Applied force * duration of force. The change in momentum during a collision.
Equal in opposite directions.
J = F * t.
Units: N*s.
Conservation of Momentum in Collisions For each body involved in a collision, its change in
momentum (ΔL) is equal to the impulse applied (J) to it. Both bodies will have the same change
in momentum, but the change in velocity can be different.
Since the impulse applied to each body is equal in magnitude and opposite in direction, their
changes in momentum are equal in magnitude and opposite in direction.
J = ΔL.
Friction Resistance to motion that dissipates energy - it is transformed into another form.
Can be external and internal.
External Friction Occurs between objects in contact. Can be sliding, rolling, or fluid drag.
Sliding Friction Applies to objects sliding over one another.
, Rolling Resistance Applies to wheels rolling over a surface.
Fluid Drag Applies to objects moving through fluids.
Internal Friction (Viscosity) Occurs during deformation.
Angular Kinetics The big difference is that inertia is no longer mass - instead, we use
moment of inertia. How forces cause acceleration is also quite different. Quantities and laws
are very similar to those of linear kinetics.
Moment of Inertia (Ip) A body's rotational inertia - its resistance to angular acceleration
(rotation). Depends on mass and spatial distribution relative to any potential axis-of-rotation. A
point of mass further from the axis-of-rotation has to linearly accelerate more to rotate with
the same angular velocity. Outer molecules need to travel a further distance, making them
harder to speed up. So, the further away from the axis-of-rotation something is, the more
resistance of rotation and more inertia it has.
Resistance of rotation is proportional to mass and distance from axis squared.
Units: kg*m^2.
Rotation of a Free Body A linear force can make a body free in space rotate about its centre-
of-mass (CoM) only if it is not in line with that CoM.
Rotation Around a Fixed Centre-of-Rotation (CoR) A linear force can make a body rotate
about a fixed point (attachment) of the body only if it is not in line with that fixed CoR.
Moment of a Force (Mp) A measure of a force's tendency to cause rotation about a point or
axis. Often called moment (M) or torque (T).
∑Mp = Ip * a.
Units: N*m.
Law of Reaction (Newton's 3rd Law) Material bodies push back when pushed. Whenever
one material body exerts a force on another material body through contact or adhesion, the
second body exerts a force of equal magnitude and opposite direction on the first body.
Collision The duration of contact between two or more bodies. Depends on elasticity - the
higher the elasticity, the lesser the duration of contact. Duration of contact is equal for both
bodies. Force (contact and reaction) is equal for both bodies, just in opposite directions. When
two or more material bodies are in contact (collide), they can accelerate or deform.
Impulse (J) Applied force * duration of force. The change in momentum during a collision.
Equal in opposite directions.
J = F * t.
Units: N*s.
Conservation of Momentum in Collisions For each body involved in a collision, its change in
momentum (ΔL) is equal to the impulse applied (J) to it. Both bodies will have the same change
in momentum, but the change in velocity can be different.
Since the impulse applied to each body is equal in magnitude and opposite in direction, their
changes in momentum are equal in magnitude and opposite in direction.
J = ΔL.
Friction Resistance to motion that dissipates energy - it is transformed into another form.
Can be external and internal.
External Friction Occurs between objects in contact. Can be sliding, rolling, or fluid drag.
Sliding Friction Applies to objects sliding over one another.
, Rolling Resistance Applies to wheels rolling over a surface.
Fluid Drag Applies to objects moving through fluids.
Internal Friction (Viscosity) Occurs during deformation.
Angular Kinetics The big difference is that inertia is no longer mass - instead, we use
moment of inertia. How forces cause acceleration is also quite different. Quantities and laws
are very similar to those of linear kinetics.
Moment of Inertia (Ip) A body's rotational inertia - its resistance to angular acceleration
(rotation). Depends on mass and spatial distribution relative to any potential axis-of-rotation. A
point of mass further from the axis-of-rotation has to linearly accelerate more to rotate with
the same angular velocity. Outer molecules need to travel a further distance, making them
harder to speed up. So, the further away from the axis-of-rotation something is, the more
resistance of rotation and more inertia it has.
Resistance of rotation is proportional to mass and distance from axis squared.
Units: kg*m^2.
Rotation of a Free Body A linear force can make a body free in space rotate about its centre-
of-mass (CoM) only if it is not in line with that CoM.
Rotation Around a Fixed Centre-of-Rotation (CoR) A linear force can make a body rotate
about a fixed point (attachment) of the body only if it is not in line with that fixed CoR.
Moment of a Force (Mp) A measure of a force's tendency to cause rotation about a point or
axis. Often called moment (M) or torque (T).
∑Mp = Ip * a.
Units: N*m.
