How much ARP requests need to single IP address?

Hello,
In Linux kernel by adding debug statement i observe that if i ping to
host 10.0.0.5 with 10 packets then first i know network stack require
to resolve hosts IP to its Hardware ID by sending ARP on Ethernet LAN.
But then what i get that if i again ping for another 10 packets to
10.0.0.5 then ARP routine is called.
Why? Why linux kernel is not caching it. Infact its caching i check it
in debug statements then why network stack require to resolve 10.0.0.5
host to send packets to it?

Also i want to know once eth_header_cache called then all successive
packet to that cache host goes directly from hh->hh_output(skb) to
hard_start_xmit?
regards,
cranium