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2 things.
1) Additionally, the area where that acceleration is focused on is quite important! That is why displacement is essential in most protective gear. From helmets to airbags to bullet proof vests.
2) "A large object hitting you slowly will carry a lot of energy but not deliver much force." That is not true.
F=m.a but the times of impact are the same for both parties (for the one hitting and the one being hit). So what matters is the momentum the change in momentum. Two parties so the change of one is (in absolute terms) the equeal to the other
m1 x Δv1 = -m2 x Δv2
m being mass and v being velocity. If m1 is big enough (or m2 small enough, what matters is the differential), even if the v1 is small the impact on 2 can be big.
Force was the wrong word, I meant impulse. An object with a large mass but very low velocity could take the same force to bring to a halt as a small object with a high velocity but will not cause damage.