Science · Grades 7–8
Motion & energy · Formula sheet
Rules, conditions and small examples in one printable reference.
Remember this
Newton’s second law
Use the net force and consistent SI units for a constant-mass object.
F_net = ma
42 × 13 = 546 N
Acceleration
Velocities include direction; a negative result can represent decreasing positive velocity.
a_avg = (v_f − v_i)/Δt
(-3 − 3)/3 = -2
Displacement at constant velocity
Displacement is signed; distance is the length of the path.
Δx = vΔt
15 × 16 = 240
Gravitational potential energy
Height is measured above the chosen reference level. Use the value of g stated in the question.
ΔE_p = mgΔh (constant g)
8 × 10 × 1 = 80
Mechanical work
For a constant force parallel to displacement, cos θ = 1.
W = Fd cos θ
28 × 34 = 952
Power
One watt is one joule per second.
P_avg = energy transferred / time
192 ÷ 12 = 16
Pressure and force
Force is perpendicular to the surface; pascals are newtons per square metre.
p = F/A
615 ÷ 5 = 123
Energy efficiency
Useful output cannot exceed total input in this simple energy accounting model.
efficiency % = useful output / input × 100
615/4100 × 100 = 15%
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Learning preview · teacher review required. Grade bands are approximate, not official curriculum alignment.